So how to deal with that?
1. Start Firefox in Safe Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance/Themes). To do the Safe mode, follow these steps:
2. Various Web Developer tools each have their own pref on the about:config page to enable or disable them.
Follow these steps:
Set those configs to false on the about:config page to disable the Scratchpad. All you need to do is just double click on those settings to toggle it true/false.
That should work. If it doesn’t, then you can try to reset your Firefox settings back to its factory default :)