I found that allowing scripts a bit more time before Firefox gives up on them helps. I use these settings in about:config:

• dom.max_chrome_script_run_time = 30
• dom.max_script_run_time = 20

Thanks. Finally got around to trying your fix. I had done that with the script, as Firefox help recommends, but not for chrome_script. Anyway, that did not solve it. What next?

Can I uninstall Firefox to solve it?

You can try uninstalling, and reinstalling Firefox (make sure you don't delete your personal information when you uninstall unless you have a backup).

If that doesn't work, try to create a new profile, and see if everything works a bit better there. Profile Manager - Create, remove or switch Firefox profiles. basically this will create a new profile that has all Firefox defaults, without any of your customized data. Your old data will still be there in another profile. If it works in the new profile, then try transferring your data from your old profile to your new one. Recovering important data from an old profile