It could be the work of one of your add-ons, or it could be '''Hardware Acceleration&#46; ''' ''[https://support&#46;mozilla&#46;org/en-US/kb/forum-response-disable-hardware-acceleration How to disable Hardware Acceleration]'' {web link} Type '''about:addons'''<enter> in the address bar to open your Add-ons Manager&#46; Hot key; '''<Control> ''(Mac=<Command>)'' <Shift> A) ''' In the Add-ons Manager, on the left, select '''Extensions&#46; ''' Disable a few add-ons, then '''Restart Firefox&#46; ''' Some added toolbar and anti-virus add-ons are known to cause Firefox issues&#46; '''Disable All Of them&#46; ''' If the problem continues, disable some more (restarting FF)&#46; Continue until the problem is gone&#46; After, you know what group is causing the issue&#46; Re-enable the last group '''ONE AT A TIME''' (restarting FF) until the problem returns&#46; Once you think you found the problem, disable that and re-enable all the others, then restart again&#46; Let us know who the suspect is, detective&#46;