What web pages is this occurring on? Have you tried to reset Firefox? [[Reset Firefox – easily fix most problems]] A few other basic trouble shooting things you can try is this: Run all Windows Updates, install all needed service packs, etc. Update your graphics driver (Firefox uses your graphics card for some rendering, and an out of date graphics card driver can cause problems. [https://support.mozilla.org/en-US/kb/how-do-i-upgrade-my-graphics-drivers https://support.mozilla.org/en-US/kb/how-do-i-upgrade-my-graphics-drivers]. Update all your plugins (Flash, Java, etc.): [http://www.mozilla.org/plugincheck/ http://www.mozilla.org/plugincheck/]. Download and Install MalwareBytes Anti-Malware, run a full Scan. [http://www.malwarebytes.org/ http://www.malwarebytes.org/]. This helps check that there are no viruses on your computer causing issues. You can uninstall this program after you clean off any infections.