When you first update to a new version of Firefox, it will run a Compatibility test to disable add-ons and plugins not able to run on that Firefox version.

It will check each add-on and plugin one at a time. The name of the add-on currently being checked will be displayed somewhere on the Compatibility Check window.

Does it get stuck on a specific add-on? If so, please post the name of it so I can help you to remove it from your computer.

You may want to try a clean uninstall or downgrading to another version of Firefox.

can you try the full installer?

• https://www.mozilla.org/en-US/firefox/all/

There are no plugin names being shown during the check. The green bar keeps moving rather than freezes.

I tried the full installer option suggested by Waka_Flocka_Flame but the result is exactly the same - it just gets stuck at the Check Add Ons stage (it has been there for more than three hours so far) - the cancel button won't work and the only way out is to shut it down with Program Manager, which says that it isn't responding.

As, following a suggestion I found somewhere else, I have completely deleted the old Mozilla Firefox folder, there should be no Add Ons to check I wouldn't have thought.

Where would I locate a previous version of Firefox to see if that installs?

Thanks

Cancel the operation of checking the plugins or create a new profile with out addons and see if it works.

• Profile Manager - Create, remove or switch Firefox profiles

It is possible that there is a problem with the file(s) that store the extensions registry.

Delete the extensions.* files (e.g. extensions.sqlite, extensions.ini) and compatibility.ini in the Firefox profile folder to reset the extensions registry.

• https://support.mozilla.org/kb/Profiles

New files will be created when required.

See "Corrupt extension files":

• http://kb.mozillazine.org/Unable_to_install_themes_or_extensions
• https://support.mozilla.org/kb/Unable+to+install+add-ons

If you see disabled or not compatible extensions in "Firefox/Tools > Add-ons > Extensions" then click the Tools button at the left end side of the Search Bar to check if there is a compatibility update available.

If this hasn't helped then also delete the addons.sqlite file.

I'm getting very confused (but I'm in my 60s and am not a techie, so maybe it's to be expected...

I can't "Cancel the operation of checking the plugins" as the CANCEL button does nothing. The only way I can do that is with Windows Program Manager, where it tells me that it's "Not Responding" so I "End Task" and finally it shuts down.

If I then run the Profile Manager, absolutely nothing happens...

"If the Profile Manager window does not open, Firefox may have been running in the background, even though it was not visible. Close all instances of Firefox or restart the computer and then try again."

As far as I can see, at this point in the proceedings, Firefox isn't running - it's not showing anywhere and I have no idea how to find it if it is 'in the background'.

I'd really like to retain the Bookmarks and Passwords, and probably some other things I don't understand, if I can (it's an old age/memory problem - all the important birthdays were in ReminderFox for example), so I have created a backup copy of the profiles folder on a memory stick in hope...

Within Application Data\Mozilla\Firefox\Profiles\uxbwtgou.default, there are five extensions files - extensions.ini, extensions.log, extensions.rdf, extensions.sqlite and extensions.sqlite-journal...

Do I delete all of these?

Thanks

You can try to delete those and see what happens, if profile corruption happens, ensure the files are in the recycle bin.

That's fixed it...

Thanks to all of you for your help - not only is it now working but I learned a few things along the way...

Duncan