Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the add-ons is causing the problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).

• Don't make any changes on the Safe mode start window.

See:

• Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems
• Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

If it does work in Safe-mode then disable all extensions and then try to find which is causing it by enabling one at a time until the problem reappears.

• Use "Disable all add-ons" on the Safe mode start window to disable all extensions.
• Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")

What I don't understand is... If I haven't added any new plug-ins or themes or anything else, all I've done is update Ff (something that Mozilla suggest as a security measure) Why as a user am I now expected to go through the need to try and rule out all these things? Surely the fault is with the update?? In fact since I upgraded, Ff has mini freezes, my mouse doesn't always scroll, I can't stop switching to new tab when opened, but sometimes it doesn't (what I wanted anyway) I can no longer use middle click on my mouse.

Now I've seen the advice, re-install mouse driver etc, yet it works with everything but Ff, when the mouse stops responding so does my keyboard, I can be in mid type and it stops entering what I type. The most annoying thing is that since Ff upgraded it is impacting on some other programs too.

The only thing stopping me switching to another browser (permanently) is Ad block and believe me if I can find this feature in Chrome, I'm gone.

Extensions can always update and are not guaranteed to work all the time. If you encounter weird effects after updating then the most likely cause is a problem with an add-on and you should check that first.

I started having problems when I updated Ff, not after upgrading my plug-ins or add-ons. I have had the same few add-ons for a few years and I only tend to update them when Ff updates and they stop working

I have been having the same problem for a few days. Couldn't find a solution anywhere so re-installed Firefox twice. Still didn't resolve the issue. Then found this page and decided to disable the DivX plug-ins and add-ons, and it's working fine now. I had updated some DivX codecs recently. Unfortunately, I already lost all my customizations during the second re-install thinking it might have to do something with that. Oh well...Does this help anybody else?

I have the same problem. The strange thing is that when I came after I installed DivX plug-ins and add-ons from this site.

Remove DivX plug-ins and add-on and restart Ff. I did and the problem is resolved.