Change the setting in about:config for this item: * http://kb.mozillazine.org/Browser.cache.check_doc_frequency

That should only happen if you open tabs in the background and haven't visited them yet during the current session.<br /> It shouldn't happen for tabs that you've already visited during the current session. ---- Start Firefox in <u>[[Safe Mode|Safe Mode]]</u> 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). *Don't make any changes on the Safe mode start window. *https://support.mozilla.org/kb/Safe+Mode *https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

Thanks!