hi, i think you might be seeing the same issue as https://bugzilla.mozilla.org/show_bug.cgi?id=1305436 which we are trying to track down at the moment...

would you be able to install this test build and report back if you just get the UI to open with it (even though it may be non-functional)?: https://archive.mozilla.org/pub/firefox/try-builds/archaeopteryx@coole-files.de-3d23b6dfd423f4dfef4dac906719720267d9fc6a/try-win32/firefox-52.0a1.en-US.win32.installer.exe

Sorry,

The UI does not open. Only visible in task manager

thank you, could you also tell us what security software you are runnin gon the device?

I am using Kaspersky Anit-Virus

thank you, i'll probably come back and ask you to test another batch of builds in a bit. it would be great if you could follow up then again, so that we might get to the bottom of this issue (it seems to be rather strange so far)...

hi again, could you please try to run these 3 builds and report back with the results of each, if you are at least able to get the interface to open?:

• build 1
• build 2
• build 3

Build 1 Opens the interface - Not possible to go to websites - Tab opens to ask for Kaspersky Add-on update (see attached) Build 2 Opens the interface - Not possible to go to websites - Does open my standard page (locally stored html-page with links) Build 3 Opens the interface - Not possible to go to websites - Does open my standard page (locally stored html-page with links) - I closed it and tried to open it again using the desktop shortcut. I get the message firefox was not closed. (I did not test this for the other builds)

Each time I uninstalled Nightly with CCleaner before installing a new version

many thanks, so this testing narrows it down to one single code-change that has apparently introduced this issue. i have put that info in the associated bug report and hope that it is now possible for developers to come up with a fix soon.

the issue is quite puzzling. in a logfile that we got from another user, the networking team identified a problem with a hanging event loop that could totally explain the symptoms you were seeing - however the build-by-build testing that we did here in this support.mozilla.org thread with your help points to a totally different code-change that first introduced the problem of firefox not starting.

so now we have two avenues to explore: first we manually created a build based on the current beta branch with just the one code-change backed out (that's the one we suspect based on the manual regression testing). it would be https://archive.mozilla.org/pub/firefox/try-builds/archaeopteryx@coole-files.de-73d579235407a1cd599845897d18cea974fb5a50/try-win32/firefox-50.0.en-US.win32.installer.exe & i'd be glad if you can test if it's opening/connecting again...

in parallel the networking team is patching the problem they see in the log and might come up with another try build containing a fix for that separate issue a little bit later today.

I have tried the last build. The interface does not open.

a build with the presumptive networking fix just arrived - do we get lucky this time (does it launch/connect)?: https://archive.mozilla.org/pub/firefox/try-builds/dd.mozilla@gmail.com-51836a9c48ad0fb657dadcc3f79444ea0d73425f/try-win32/firefox-52.0a1.en-US.win32.installer.exe

It works perfect!

Many thanks!

thanks for following up with us & confirming - at this point this was just a test build, but i will follow up once i know when/how the fix makes its way into firefox release or beta...

hi, mozilla just released an update to firefox 49.0.2 that should fix a problem that sound pretty similar to what you've described. you can download this new version from https://www.mozilla.org/en-US/firefox/all/ to see if it works for you too.

Thanks 49.0.2 is working perfectly.

Good job & thx for the assistance and keeping me posted!