Hi sidonius, I think I answered another thread you posted already. I'd try starting Firefox in [[Safe Mode]]. If you don't have the issue while all of your add-ons, extensions, and themes are disabled, you can try adding them back in one by one until you find the culprit. You should look at the [https://support.mozilla.org/en-US/kb/Troubleshooting-extensions-themes Extensions and Themes troubleshooting guide ] and the [[Troubleshooting plugins]] article as well. Hopefully this helps!