Hi callfrankplumber, I don't know why changing from English US to English UK on the Options page (I assume) would have any ill effects. There probably is something else going on.

First, if you haven't since the problem began, could you do a normal Windows shutdown and restart, to free up any locked files and complete any pending updates?

Then if Firefox won't start normally, could you try starting it in its Safe Mode:

Hold down the Shift key when starting Firefox. (On Mac, hold down the option/alt key instead of the Shift key.)

A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement in stability?

Regarding Firefox Sync, it's hard to know what is there and what you will get in a new profile. Some users report a seamless experience, others have problems. But as long as your existing Firefox profile folder hasn't been deleted, you can use a local bookmark backup file if you need to create a new profile. More on that if needed.

Hi jscher2000, Opening in Safe Mode did indeed allow Firefox to open, and my Bookmarks were all there too. What a temporary relief! However, when I tried to open Firefox normally it still 'flashed' open momentarily and crashed.

1. Any suggestions on how I can fix this more permanently?

2. Yes, I would appreciate it if you could tell me how I can save my Bookmarks locally.

3. If I can save all my bookmarks locally, might it be worth uninstalling, reinstalling and somehow adding my Bookmarks back again?

Many thanks in anticipation, Frank Ojay

Hi Frank, if you start up in Firefox's Safe Mode again, you can create a backup of your bookmarks in two different formats:

• "JSON" backup format: Restore bookmarks from backup or move them to another computer
• "HTML" export format: Export Firefox bookmarks to an HTML file to back up or transfer bookmarks

As a test, try disabling Firefox from using hardware acceleration. It is automatically disabled in Firefox's Safe Mode, so this change will have it disabled when you start up in regular mode. The steps are in this article: Firefox's performance settings.

Does that help avoid the crashes, or still crashing?

(I don't think you should uninstall yet until we have more leads on what is going on.)

Hello Jefferson, Thanks for getting back to me. I successfully followed your directions and made a manual backup of my Bookmarks. I also disabled hardware acceleration and tried to restart Firefox, but alas without success. What next, do you think? Regards, Frank

The other things Firefox's Safe Mode changes are:

• All Extensions are disabled
• userChrome.css and userContent.css file are disabled (optional configuration files)
• JavaScript "just in time" compilers are disabled

So you could try fully disabling all non-essential extensions while you're in Firefox's Safe Mode and see whether that makes any difference.

Also:

New Profile Test

This takes about 3 minutes, plus the time to test whether it can start up.

Inside Firefox, type or paste about:profiles in the address bar and press Enter/Return to load it.

Click the "Create a New Profile" button, then click Next. Assign a name like Oct2019, ignore the option to relocate the profile folder, and click the Finish button.

After creating the profile, scroll down to it and click the Launch profile in new browser button.

Firefox should open a new window that looks like a brand new, uncustomized installation. (Your existing Firefox window(s) should not be affected.) Please ignore any tabs enticing you to connect to a Sync account or to activate extensions found on your system so we can get a clean test.

Does Firefox run or crash in the new profile?

When you are done with the experiment, you can close the extra window without affecting your regular Firefox profile. (Oct2019 will remain available for future testing.)

Are you using the en-US Firefox version with the en-GB language pack or did you install the en-GB Firefox version?

If you have submitted crash reports then please post the IDs of one or more recent crash reports that start with "bp-".

• bp-xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx

You can find the report ID of recent crash reports on the "Help -> Troubleshooting Information" (about:support) page.

• click the "All Crash Reports" button on this page to open the about:crashes page and see all crash reports.

Alternatively you can open about:crashes via the location/address bar.

See also:

• https://support.mozilla.org/en-US/kb/Mozilla+Crash+Reporter

Hello Jefferson, I was able to get away from my computer over the weekend, so I've only returned to sorting out Firefox now. The problem may be solved, but I just wanted to check with you that I've done the right thing.

1. I looked to see if I had any 'extensions' and didn't really see anything - I'm not an expert IT user.

2. I followed the directions for creating a new profile. This gave me a stable Firefox and I've restored all my bookmarks from your previous directions!

3. However, I'm not sure now which 'profile' Firefox is working on and need I worry about this? Should I just carry on with the new profile?

You've been a great help, Jefferson - many thanks indeed! Kind regards, Frank

Hi Frank, if you use the "Set as default profile" button for your new profile on the about:profiles page, you can be sure which profile Firefox will start up in the next time.

As for what ails the old one, I don't know whether it is worth taking the time to research at this point??