If you have Nvidia graphics, could you try disabling the "off main thread composition" (OMTC) feature introduced in Firefox 33? The steps are as follows: (1) In a new tab, type or paste '''about:config''' in the address bar and press Enter. Click the button promising to be careful. (2) In the search box above the list, type or paste '''layers''' and pause while the list is filtered (3) Double-click the '''layers.offmainthreadcomposition.enabled''' preference to switch it from true to false I can't recall whether that takes effect immediately or only after you exit Firefox and start it up again (since I don't have the symptoms to test with). ---- If you do not have Nvidia graphics, or if the above is not helpful, could you test in Firefox's Safe Mode? In Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem. ''If Firefox is not running:'' Hold down the Shift key when starting Firefox. ''If Firefox is running:'' You can restart Firefox in Safe Mode using either: * "3-bar" menu button > "?" button > Restart with Add-ons Disabled * Help menu > Restart with Add-ons Disabled and OK the restart. ''Both scenarios:'' A small dialog should appear. Click "Start in Safe Mode" (''not'' Refresh). Any improvement?