Either something is indeed blocking updates, or app.update.url preference is not correctly set. It should be https://aus.thunderbird.net/update/6/%PRODUCT%/%VERSION%/%BUILD_ID%/%BUILD_TARGET%/%LOCALE%/%CHANNEL%/%OS_VERSION%/%SYSTEM_CAPABILITIES%/%DISTRIBUTION%/%DISTRIBUTION_VERSION%/update.xml

Another thing to look at - check preferences > show update history

Thank you. app.update.url is exactly as you posted, and Show Update History shows only up to 78.7.0, installed on Jan 29. However, the version installed is, indeed, 78.9.1.

Firefox has no problem navigating to https://aus5.mozilla.org/update/6/ https://aus5.mozilla.org/update/6/ (I get "This XML file does not appear to have any style information associated with it. The document tree is shown below."), so the URL itself is not blocked.

Is there a way to actually debug what is happening here?

Another bit: clicking Check for Updates gives me the result Thunderbird is up to date. However, leaving Thunderbird running for some time (don't know if it's 15 minutes or 1 hour) will invariably produce a green arrow at about the top right-hand corner of the application window and/or a complaint about the inability to download updates.

please do edit > preferences type in edit and click "config editor" paste in app.update.log and change it to true (create boolean app.update.log if it does not already exist) restart thunderbird

do help > about or do some other action to force an update check. check tools > developer > error console for relevant error and post them ere

Thank you. I don't know what parts are more relevant than others but I do know that if I expand all the exceptions, I will run out of the space allocated for the response here. So, I have collapsed all exceptions.

I can see that the update URL that the updater ends up trying is "https://aus.thunderbird.net/update/6/Thunderbird/78.9.1/20210406220621/WINNT_x86_64-msvc-x64/en-US/release/Windows_NT%2010.0.0.0.19042.928%20(x64)/ISET:SSE4_2,MEM:65473/default/default/update.xml?force=1" and I can see, when navigating to that with Firefox, that it will not return any XML file. I do not know why it is important to pass information about the instruction set or the amount of memory in the request, but I can see that they are in the request.

EDIT: I know that the application is installed in the Program Files (x86) folder but it really is the 64-bit build. Why it is in the x86 folder, I do not know.

[Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsIXPCComponents_Utils.readUTF8URI]" nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)" location: "JS frame :: resource://gre/modules/L10nRegistry.jsm :: L10nRegistry.loadSync :: line 658" data: no] L10nRegistry.jsm:658:19 [Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsIXPCComponents_Utils.readUTF8URI]" nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)" location: "JS frame :: resource://gre/modules/L10nRegistry.jsm :: L10nRegistry.loadSync :: line 658" data: no] L10nRegistry.jsm:658:19 [l10nregistry] Attempting to synchronously load file

           resource:///chrome/en-US/locale/en-US/calendar/messenger/openpgp/msgReadStatus.ftl while it's being loaded asynchronously. L10nRegistry.jsm:563:19

[Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsIXPCComponents_Utils.readUTF8URI]" nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)" location: "JS frame :: resource://gre/modules/L10nRegistry.jsm :: L10nRegistry.loadSync :: line 658" data: no] L10nRegistry.jsm:658:19 [Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsIXPCComponents_Utils.readUTF8URI]" nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)" location: "JS frame :: resource://gre/modules/L10nRegistry.jsm :: L10nRegistry.loadSync :: line 658" data: no] L10nRegistry.jsm:658:19 TypeError: singletons is null 3 ActorManagerChild.jsm:297:32 [Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsIXPCComponents_Utils.readUTF8URI]" nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)" location: "JS frame :: resource://gre/modules/L10nRegistry.jsm :: L10nRegistry.loadSync :: line 658" data: no] L10nRegistry.jsm:658:19 [Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsIXPCComponents_Utils.readUTF8URI]" nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)" location: "JS frame :: resource://gre/modules/L10nRegistry.jsm :: L10nRegistry.loadSync :: line 658" data: no] L10nRegistry.jsm:658:19 Error while loading 'jar:file:///C:/Program%20Files%20(x86)/Mozilla%20Thunderbird/omni.ja!/chrome/messenger/search-extensions/twitter/manifest.json' (NS_ERROR_FILE_NOT_FOUND) Extension.jsm:570 1618806965918 addons.xpi WARN Exception running bootstrap method startup on twitter@search.mozilla.org: Error: Error while loading 'jar:file:///C:/Program%20Files%20(x86)/Mozilla%20Thunderbird/omni.ja!/chrome/messenger/search-extensions/twitter/manifest.json' (NS_ERROR_FILE_NOT_FOUND)(resource://gre/modules/Extension.jsm:570:20) JS Stack trace: readJSON/</<@Extension.jsm:570:20 onStopRequest@NetUtil.jsm:128:18 OverrideError: An entry font-size-label of type message is already defined in this bundle OverrideError: An entry window-close-key of type message is already defined in this bundle OverrideError: An entry startup-label of type message is already defined in this bundle OverrideError: An entry focus-search-shortcut of type message is already defined in this bundle OverrideError: An entry close-button of type message is already defined in this bundle OverrideError: An entry font-size-label of type message is already defined in this bundle OverrideError: An entry window-close-key of type message is already defined in this bundle OverrideError: An entry startup-label of type message is already defined in this bundle OverrideError: An entry focus-search-shortcut of type message is already defined in this bundle OverrideError: An entry close-button of type message is already defined in this bundle [Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsIXPCComponents_Utils.readUTF8URI]" nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)" location: "JS frame :: resource://gre/modules/L10nRegistry.jsm :: L10nRegistry.loadSync :: line 658" data: no] L10nRegistry.jsm:658:19 [Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsIXPCComponents_Utils.readUTF8URI]" nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)" location: "JS frame :: resource://gre/modules/L10nRegistry.jsm :: L10nRegistry.loadSync :: line 658" data: no] L10nRegistry.jsm:658:19 NS_ERROR_ABORT: Certificate issuer is not built-in. CertUtils.jsm:183 NotSupportedError: CustomElementRegistry.define: 'conversation-browser' has already been defined as a custom element conversation-browser.js:853 Empty string passed to getElementById(). 2 browser-custom-element.js:411:22 AUS:SVC UpdateService:removeDownloadListener - no downloader! AUS:SVC isServiceInstalled - returning true AUS:SVC shouldUseService - returning true AUS:SVC getCanStageUpdates - able to stage updates using the service AUS:SVC isServiceInstalled - returning true AUS:SVC shouldUseService - returning true AUS:SVC getCanStageUpdates - able to stage updates using the service AUS:SVC Checker: checkForUpdates, force: true AUS:SVC UpdateService.canCheckForUpdates - able to check for updates AUS:SVC Checker:getUpdateURL - update URL: https://aus.thunderbird.net/update/6/Thunderbird/78.9.1/20210406220621/WINNT_x86_64-msvc-x64/en-US/release/Windows_NT%2010.0.0.0.19042.928%20(x64)/ISET:SSE4_2,MEM:65473/default/default/update.xml?force=1 AUS:SVC Checker:checkForUpdates - sending request to: https://aus.thunderbird.net/update/6/Thunderbird/78.9.1/20210406220621/WINNT_x86_64-msvc-x64/en-US/release/Windows_NT%2010.0.0.0.19042.928%20(x64)/ISET:SSE4_2,MEM:65473/default/default/update.xml?force=1 NS_ERROR_ABORT: Certificate issuer is not built-in. CertUtils.jsm:183 AUS:SVC Checker:onLoad - request completed downloading document AUS:SVC Checker:onLoad - Getting sslStatus failed. AUS:SVC Checker:onLoad - there was a problem checking for updates. Exception: TypeError: this._request.responseXML is null AUS:SVC Checker:onLoad - request.status: 302 AUS:SVC getStatusTextFromCode - transfer error: Update XML file not found (404), default code: 404 NS_ERROR_NOT_AVAILABLE: ActivityManager.jsm:127 UTM:SVC TimerManager:registerTimer - timerID: telemetry_modules_ping interval: 604800 skipFirst: true UTM:SVC TimerManager:registerTimer - timerID: telemetry_untrustedmodules_ping interval: 86400 skipFirst: false AUS:SVC UpdateService:removeDownloadListener - no downloader! </p>

​

Thank you. My response vaporized into thin air. Attempt #3.

If all exceptions are expanded, the response will not fit in my allotted quota. The installation folder is x86 but the build is 64-bit. I don't know why that folder was chosen. The updater seems to come up with the URL https://aus.thunderbird.net/update/6/Thunderbird/78.9.1/20210406220621/WINNT_x86_64-msvc-x64/en-US/release/Windows_NT%2010.0.0.0.19042.928%20(x64)/ISET:SSE4_2,MEM:65473/default/default/update.xml?force=1, and when I navigate to that URL with Firefox, I get no XML file. I do not know why it is important to pass information about the supported instruction sets or amount of memory in the URL but I can see that they are there.

[Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsIXPCComponents_Utils.readUTF8URI]" nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)" location: "JS frame :: resource://gre/modules/L10nRegistry.jsm :: L10nRegistry.loadSync :: line 658" data: no] L10nRegistry.jsm:658:19 [Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsIXPCComponents_Utils.readUTF8URI]" nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)" location: "JS frame :: resource://gre/modules/L10nRegistry.jsm :: L10nRegistry.loadSync :: line 658" data: no] L10nRegistry.jsm:658:19 [l10nregistry] Attempting to synchronously load file

           resource:///chrome/en-US/locale/en-US/calendar/messenger/openpgp/msgReadStatus.ftl while it's being loaded asynchronously. L10nRegistry.jsm:563:19

[Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsIXPCComponents_Utils.readUTF8URI]" nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)" location: "JS frame :: resource://gre/modules/L10nRegistry.jsm :: L10nRegistry.loadSync :: line 658" data: no] L10nRegistry.jsm:658:19 [Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsIXPCComponents_Utils.readUTF8URI]" nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)" location: "JS frame :: resource://gre/modules/L10nRegistry.jsm :: L10nRegistry.loadSync :: line 658" data: no] L10nRegistry.jsm:658:19 TypeError: singletons is null 3 ActorManagerChild.jsm:297:32 [Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsIXPCComponents_Utils.readUTF8URI]" nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)" location: "JS frame :: resource://gre/modules/L10nRegistry.jsm :: L10nRegistry.loadSync :: line 658" data: no] L10nRegistry.jsm:658:19 [Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsIXPCComponents_Utils.readUTF8URI]" nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)" location: "JS frame :: resource://gre/modules/L10nRegistry.jsm :: L10nRegistry.loadSync :: line 658" data: no] L10nRegistry.jsm:658:19 Error while loading 'jar:file:///C:/Program%20Files%20(x86)/Mozilla%20Thunderbird/omni.ja!/chrome/messenger/search-extensions/twitter/manifest.json' (NS_ERROR_FILE_NOT_FOUND) Extension.jsm:570 1618806965918 addons.xpi WARN Exception running bootstrap method startup on twitter@search.mozilla.org: Error: Error while loading 'jar:file:///C:/Program%20Files%20(x86)/Mozilla%20Thunderbird/omni.ja!/chrome/messenger/search-extensions/twitter/manifest.json' (NS_ERROR_FILE_NOT_FOUND)(resource://gre/modules/Extension.jsm:570:20) JS Stack trace: readJSON/</<@Extension.jsm:570:20 onStopRequest@NetUtil.jsm:128:18 OverrideError: An entry font-size-label of type message is already defined in this bundle OverrideError: An entry window-close-key of type message is already defined in this bundle OverrideError: An entry startup-label of type message is already defined in this bundle OverrideError: An entry focus-search-shortcut of type message is already defined in this bundle OverrideError: An entry close-button of type message is already defined in this bundle OverrideError: An entry font-size-label of type message is already defined in this bundle OverrideError: An entry window-close-key of type message is already defined in this bundle OverrideError: An entry startup-label of type message is already defined in this bundle OverrideError: An entry focus-search-shortcut of type message is already defined in this bundle OverrideError: An entry close-button of type message is already defined in this bundle [Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsIXPCComponents_Utils.readUTF8URI]" nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)" location: "JS frame :: resource://gre/modules/L10nRegistry.jsm :: L10nRegistry.loadSync :: line 658" data: no] L10nRegistry.jsm:658:19 [Exception... "Component returned failure code: 0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH) [nsIXPCComponents_Utils.readUTF8URI]" nsresult: "0x80520001 (NS_ERROR_FILE_UNRECOGNIZED_PATH)" location: "JS frame :: resource://gre/modules/L10nRegistry.jsm :: L10nRegistry.loadSync :: line 658" data: no] L10nRegistry.jsm:658:19 NS_ERROR_ABORT: Certificate issuer is not built-in. CertUtils.jsm:183 NotSupportedError: CustomElementRegistry.define: 'conversation-browser' has already been defined as a custom element conversation-browser.js:853 Empty string passed to getElementById(). 2 browser-custom-element.js:411:22 AUS:SVC UpdateService:removeDownloadListener - no downloader! AUS:SVC isServiceInstalled - returning true AUS:SVC shouldUseService - returning true AUS:SVC getCanStageUpdates - able to stage updates using the service AUS:SVC isServiceInstalled - returning true AUS:SVC shouldUseService - returning true AUS:SVC getCanStageUpdates - able to stage updates using the service AUS:SVC Checker: checkForUpdates, force: true AUS:SVC UpdateService.canCheckForUpdates - able to check for updates AUS:SVC Checker:getUpdateURL - update URL: https://aus.thunderbird.net/update/6/Thunderbird/78.9.1/20210406220621/WINNT_x86_64-msvc-x64/en-US/release/Windows_NT%2010.0.0.0.19042.928%20(x64)/ISET:SSE4_2,MEM:65473/default/default/update.xml?force=1 AUS:SVC Checker:checkForUpdates - sending request to: https://aus.thunderbird.net/update/6/Thunderbird/78.9.1/20210406220621/WINNT_x86_64-msvc-x64/en-US/release/Windows_NT%2010.0.0.0.19042.928%20(x64)/ISET:SSE4_2,MEM:65473/default/default/update.xml?force=1 NS_ERROR_ABORT: Certificate issuer is not built-in. CertUtils.jsm:183 AUS:SVC Checker:onLoad - request completed downloading document AUS:SVC Checker:onLoad - Getting sslStatus failed. AUS:SVC Checker:onLoad - there was a problem checking for updates. Exception: TypeError: this._request.responseXML is null AUS:SVC Checker:onLoad - request.status: 302 AUS:SVC getStatusTextFromCode - transfer error: Update XML file not found (404), default code: 404 NS_ERROR_NOT_AVAILABLE: ActivityManager.jsm:127 UTM:SVC TimerManager:registerTimer - timerID: telemetry_modules_ping interval: 604800 skipFirst: true UTM:SVC TimerManager:registerTimer - timerID: telemetry_untrustedmodules_ping interval: 86400 skipFirst: false AUS:SVC UpdateService:removeDownloadListener - no downloader! OverrideError: An entry font-size-label of type message is already defined in this bundle OverrideError: An entry window-close-key of type message is already defined in this bundle OverrideError: An entry startup-label of type message is already defined in this bundle OverrideError: An entry focus-search-shortcut of type message is already defined in this bundle OverrideError: An entry close-button of type message is already defined in this bundle OverrideError: An entry font-size-label of type message is already defined in this bundle OverrideError: An entry window-close-key of type message is already defined in this bundle OverrideError: An entry startup-label of type message is already defined in this bundle OverrideError: An entry focus-search-shortcut of type message is already defined in this bundle OverrideError: An entry close-button of type message is already defined in this bundle AUS:SVC isServiceInstalled - returning true AUS:SVC shouldUseService - returning true AUS:SVC getCanStageUpdates - able to stage updates using the service AUS:SVC isServiceInstalled - returning true AUS:SVC shouldUseService - returning true AUS:SVC getCanStageUpdates - able to stage updates using the service AUS:SVC Checker: checkForUpdates, force: true AUS:SVC UpdateService.canCheckForUpdates - able to check for updates AUS:SVC Checker:getUpdateURL - update URL: https://aus.thunderbird.net/update/6/Thunderbird/78.9.1/20210406220621/WINNT_x86_64-msvc-x64/en-US/release/Windows_NT%2010.0.0.0.19042.928%20(x64)/ISET:SSE4_2,MEM:65473/default/default/update.xml?force=1 AUS:SVC Checker:checkForUpdates - sending request to: https://aus.thunderbird.net/update/6/Thunderbird/78.9.1/20210406220621/WINNT_x86_64-msvc-x64/en-US/release/Windows_NT%2010.0.0.0.19042.928%20(x64)/ISET:SSE4_2,MEM:65473/default/default/update.xml?force=1 NS_ERROR_ABORT: Certificate issuer is not built-in. CertUtils.jsm:183 AUS:SVC Checker:onLoad - request completed downloading document AUS:SVC Checker:onLoad - Getting sslStatus failed. AUS:SVC Checker:onLoad - there was a problem checking for updates. Exception: TypeError: this._request.responseXML is null AUS:SVC Checker:onLoad - request.status: 302 AUS:SVC getStatusTextFromCode - transfer error: Update XML file not found (404), default code: 404 NotSupportedError: CustomElementRegistry.define: 'conversation-browser' has already been defined as a custom element conversation-browser.js:853 Empty string passed to getElementById(). 4 browser-custom-element.js:411:22 </p>

​

Well that is a long way to get to exactly the answer folks have been getting for probably 5 years. Your anti-virus is messing with the connection.

I do not use f-secure, But these instructions are for Firefox and as Firefox and Thunderbird use exactly the same security model anything that has to be imported into Firefox also has to be imported into Thunderbird.

If you go to the options/Preferences and search for certificate you will see a manage certificates button that opens the certificate manager.

Note if update does not work, search for addons should not work in the addon manager either as both make HTTPS queries to a web server and display the resulting page in the application.

Thank you. Searching for add-ons does work. There are absolutely no problems getting results with the word attachment, for instance.

I do not use F-Secure's Threatshield feature. F-Secure's log of blocked websites contains no entries whatsoever related to Thunderbird or thunderbird.net. F-Secure's application control has nothing relevant for Thunderbird.

I do not use any solution that decrypts encrypted traffic at points other than the intended ones, using a certificate-in-the-middle approach (or any other approach, for that matter).

The instructions that you kindly linked are for an F-Secure business product, and I am using a consumer product. Do you have another idea? I would be very grateful for any.

New information: update checking will fail with the white arrow on green background only if IPv6 is disabled for the network adapter in use. If IPv6 is enabled, the white arrow on green background will not appear. New information 2: F-Secure's ThreatShield (referred to in a suggested solution above) does not apply to this case in any manner. It is a product installed in a Linux gateway and works by inspecting SSL traffic and requires a dedicated certificate to be installed. F-Secure TOTAL (including Anti-Virus) does not do this.

Bump?

Is there a way of getting a relevant response to this case? It applies also with Thunderbird 91.

TEST 1 F-Secure TOTAL apparently has a VPN Switch off the VPN and then retry updating in Thunderbird. This will indicate whether the VPN is causing the issue.

If still problem TEST 2 Exit Thunderbird Restart Computer in 'Safe Mode with Networking' Start Thunderbird Try update

Please report back on results.

Thank you for the response. I am not using the VPN part, which, in F-Secure Terms is called Freedome. I am not using any other VPN solution, either. I will now restart the computer in safe mode with networking and see what happens, including posting relevant error logs.

Updater fails in safe mode with networking, as well. Note that despite the text in the log about certificate errors, Firefox has absolutely no problem navigating to exactly the same page as the one that Thunderbird fails with. No VPN, no security software meddling in the middle. Log:

19:02:03.120 AUS:SVC Creating UpdateService 19:02:03.120 AUS:SVC Logging current UpdateService status: 19:02:03.121 AUS:SVC UpdateService.canUsuallyCheckForUpdates - able to check for updates 19:02:03.121 AUS:SVC UpdateService.canCheckForUpdates - able to check for updates 19:02:03.121 AUS:SVC getCanApplyUpdates - testing write access C:\ProgramData\Mozilla\updates\8216C80C92C4E828\update.test 19:02:03.122 AUS:SVC isServiceInstalled - returning true 19:02:03.122 AUS:SVC shouldUseService - returning true 19:02:03.122 AUS:SVC getCanApplyUpdates - bypass the write checks because the Windows Maintenance Service can be used 19:02:03.122 AUS:SVC isServiceInstalled - returning true 19:02:03.122 AUS:SVC shouldUseService - returning true 19:02:03.122 AUS:SVC getCanStageUpdates - able to stage updates using the service 19:02:03.122 AUS:SVC Elevation required: false 19:02:03.122 AUS:SVC Other instance of the application currently running: false 19:02:03.122 AUS:SVC Downloading: false 19:02:03.122 AUS:SVC End of UpdateService status 19:02:03.122 AUS:SVC isServiceInstalled - returning true 19:02:03.122 AUS:SVC shouldUseService - returning true 19:02:03.122 AUS:SVC getCanStageUpdates - able to stage updates using the service 19:02:03.122 AUS:SVC isServiceInstalled - returning true 19:02:03.122 AUS:SVC shouldUseService - returning true 19:02:03.122 AUS:SVC getCanStageUpdates - able to stage updates using the service 19:02:03.122 AUS:SVC Checker: checkForUpdates, force: true 19:02:03.122 AUS:SVC Creating UpdateService 19:02:03.122 AUS:SVC Logging current UpdateService status: 19:02:03.122 AUS:SVC UpdateService.canUsuallyCheckForUpdates - able to check for updates 19:02:03.122 AUS:SVC UpdateService.canCheckForUpdates - able to check for updates 19:02:03.122 AUS:SVC getCanApplyUpdates - testing write access C:\ProgramData\Mozilla\updates\8216C80C92C4E828\update.test 19:02:03.122 AUS:SVC isServiceInstalled - returning true 19:02:03.122 AUS:SVC shouldUseService - returning true 19:02:03.122 AUS:SVC getCanApplyUpdates - bypass the write checks because the Windows Maintenance Service can be used 19:02:03.122 AUS:SVC isServiceInstalled - returning true 19:02:03.122 AUS:SVC shouldUseService - returning true 19:02:03.122 AUS:SVC getCanStageUpdates - able to stage updates using the service 19:02:03.122 AUS:SVC Elevation required: false 19:02:03.122 AUS:SVC Other instance of the application currently running: false 19:02:03.122 AUS:SVC Downloading: false 19:02:03.122 AUS:SVC End of UpdateService status 19:02:03.122 AUS:SVC UpdateService.canUsuallyCheckForUpdates - able to check for updates 19:02:03.122 AUS:SVC UpdateService.canCheckForUpdates - able to check for updates 19:02:03.122 AUS:SVC waitForOtherInstances - beginning polling 19:02:03.122 AUS:SVC waitForOtherInstances - no other instances found, exiting 19:02:03.160 AUS:SVC Checker:getUpdateURL - update URL: https://aus.thunderbird.net/update/6/Thunderbird/91.1.0/20210902035758/WINNT_x86_64-msvc-x64/en-US/release/Windows_NT%2010.0.0.0.19042.1237%20(x64)/ISET:SSE4_2,MEM:65473/default/default/update.xml?force=1 19:02:03.161 AUS:SVC Checker:checkForUpdates - sending request to: https://aus.thunderbird.net/update/6/Thunderbird/91.1.0/20210902035758/WINNT_x86_64-msvc-x64/en-US/release/Windows_NT%2010.0.0.0.19042.1237%20(x64)/ISET:SSE4_2,MEM:65473/default/default/update.xml?force=1 19:02:03.277 NS_ERROR_ABORT: Certificate issuer is not built-in. CertUtils.jsm:183 19:02:03.439 AUS:SVC Checker:onLoad - request completed downloading document 19:02:03.439 AUS:SVC Checker:onLoad - Getting sslStatus failed. 19:02:03.439 AUS:SVC Checker:onLoad - there was a problem checking for updates. Exception: TypeError: this._request.responseXML is null 19:02:03.439 AUS:SVC Checker:onLoad - request.status: 302 19:02:03.439 AUS:SVC getStatusTextFromCode - transfer error: Update XML file not found (404), default code: 404

Click the link you posted to the aus.thunderbird.net website.

In the Firefox browser window click the padlock beside the URL. and then the > beside connection secure. Who is shown as verifying that state?

I note that the link automatically redirects to a Mozilla server, so don't take any notice of that part at this point, only who certifies the link.

Thank you for the response. The verifier is DigiCert Inc, the serial number is 07:01:CE:8F:C6:8D:4A:83:D8:81:DB:18:C5:B2:3C:D0 and the SHA-256 fingerprint is E5:D2:A0:8F:02:70:85:82:7D:88:89:24:38:81:1C:91:14:8A:11:56:E0:A0:D4:CF:FE:11:4F:22:EE:4B:1C:D7.