Please explain the problem in detail. What happens? What is the exact error messages?

Thanks for the reply. Here are three examples: 1) I login to an air transport company using Firefox. It recognises me. It identifies the flight I have already booked. But when I try to get a boarding pass (which requires more security information) the site will not accept this and stalls. There's no error message. And no problem when I do it on Microsoft Edge. 2) I login to my bank. No problem doing that, and I can see all the latest bank statements. But it won't let me see older ones. No error message. And no problem on Microsoft Edge. 3) Same as (2) but this time I want to make a transfer. I proceed to almost the last stage, but it won't go to the final stage. No error message. And no problem on Microsoft Edge.

What are the site for the air transport and bank? It could be site related where they only work with certain browser.

Make sure you are not blocking content.

Start Firefox in Safe Mode {web link}

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

One issue that seems more common lately is Firefox's Tracking Protection feature. When it is blocking content in a page, a shield icon will appear at the left end of the address bar next to the padlock icon. This article has more info on managing this feature: Tracking Protection {web link}

WestEnd said

What are the site for the air transport and bank? It could be site related where they only work with certain browser.

Thanks for your reply. The sites in my examples were EasyJet and Nationwide; but I don't think that the answer is their choice of browser. I did contact one of them about the problem. It said it couldn't think of a problem at their end, and it was the first to suggest it might be the cache on my browser.

FredMcD said

Make sure you are not blocking content. Start Firefox in Safe Mode {web link} A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

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One issue that seems more common lately is Firefox's Tracking Protection feature. When it is blocking content in a page, a shield icon will appear at the left end of the address bar next to the padlock icon. This article has more info on managing this feature: Tracking Protection {web link}

Thanks for your reply. It has produced some information: In 'Firefox Safe Mode' I tried my online bank and I could access my earlier statements (a success!). To check, I then closed from Safe Mode; reopened as normal and I could not access the earlier statements. I checked the address bar and there was not a shield, but the 'circled dot'. I opened that and it only said 'Blockable content detected on this site' (plus a shield and several options) but I suppose that means it was not actually blocking content. I have to stop for a while, but will have a look at the 'Tracking Protection' link later.

It could be the work of one of your add-ons, or it could be Hardware Acceleration. How to disable Hardware Acceleration {web link}

Type about:addons<enter> in the address bar to open your Add-ons Manager. Hot key; <Control> (Mac=<Command>) <Shift> A)

In the Add-ons Manager, on the left, select Extensions. Disable a few add-ons, then Restart Firefox.

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All Of them.

If the problem continues, disable some more (restarting FF). Continue until the problem is gone. After, you know what group is causing the issue. Re-enable the last group ONE AT A TIME (restarting FF) until the problem returns.

Once you think you found the problem, disable that and re-enable all the others, then restart again. Let us know who the suspect is, detective.

The 'Add-ons' test has solved the problem. Many Thanks. Only one Add-on was listed: Zoom Picture, version 1.0, updated 2 December 2018. I disabled it and then I was able to carry out one of the operations on my online bank, that I had not been able to do recently. Consequently, I have not pursued the 'Hardware Acceleration' suggestion. [Just for information: both the bank and the easyjet problems have occurred in this month of December and since the update time for that Add-on. I did have a problem with easyjet earlier this year, before the date of the Add-on. That was sorted when I used a different device and software; but I think I also changed the security information at the same time; and that might have been the cause of the earlier problem.] Thanks again.

That was very good work. Well done.

Contact Zoom Picture support and let them know.

Just to let you know: I have sent the details of the problem and how the source was identified to 'Zoom' via their feedback page.

Further information: The 'Zoom' I sent the information to have replied saying it's not their add-on. I found them by googling 'zoom picture'. They were the only google result that seemed likely, and they do refer to Firefox. I have attached screenshots of the correspondence to give you the details. [The images are not in chronological order - check the time of each message within the screenshots to read them in the correct order.]

The "unique ID" associated with the extension (ext@uksfdahdhsc according to your original extensions list) doesn't seem to be listed on the Mozilla Add-ons site. It may have been injected when you installed some other program or you might have picked it up from a different site.

As a precaution: Troubleshoot Firefox issues caused by malware

It’s very sad, but many software downloaders/ installers will trick you into installing not only their program, but other programs as well.

You have heard of the fine print in shady contracts, right? Well, some installers you need to look at the itsy bitsy teeny weeny fine print.

You are thinking you are giving the installer permission to install the program you want by using the recommended option. But if you use the Manual Option Instead, you discover all kinds of stuff that you do not even know what it is or what it does.

From now on, everyone needs to Use The Manual Option to put a stop to this.

Note that these programs can also change browser/computer settings.

Thanks for the previous replies. As noted, disabling the dodgy Add-on cured the problem I was aware of. I have not yet followed all of the subsequent suggestions - partly because of time and because I admit to being 'out-of-my depth' with some of these. But meanwhile, I have had another reply from Zoom Video Communications (who did not create the dodgy Add-on but whose name 'Zoom' was used by it). I have attached their reply, and it suggests it came from the URL of a Mozilla/Firefox/user. I have not opened that URL - it being suggested as the origin of the dodgy software - but perhaps someone in Mozilla might want to investigate it?

https://addons.mozilla.org/en-us/firefox/user13059652/ We're sorry, but we can't find what you're looking for.

I was told by the customer service of aliexpress.com that their website would no longer accept payment submissions from any browser other than Chrome. Is this true. Can they do that?

Meran said

I was told by the customer service of aliexpress.com that their website would no longer accept payment submissions from any browser other than Chrome. Is this true. Can they do that?

While I have not heard this, it is a little surprising. It's certainly technically possible for them to limit their sites to particular browsers, but why?

jscher2000 If you change the Browser Agent, would that fool the website?