Start Firefox in <u>[[Safe Mode|Safe Mode]]</u> to check if one of the extensions (Firefox/Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Firefox/Tools > Add-ons > Appearance). *Do NOT click the Reset button on the Safe Mode start window or otherwise make changes. *https://support.mozilla.org/kb/Safe+Mode *https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes Try to rename or delete the prefs.js file and possible numbered prefs-##.js files and a possible user.js file to reset all prefs to the default value. *http://kb.mozillazine.org/Preferences_not_saved *http://kb.mozillazine.org/Resetting_preferences

If you've had your Pin It button for a long time, could you try removing it and re-adding it from the Pinterest page to see whether the current version avoids this problem? http://about.pinterest.com/goodies/#browser ''Possibly related question: [https://support.mozilla.org/en-US/questions/964777 New update is blocking wanted pop-ups such as pinterest, which I actively use to promote my business, how do I fix this? I tried "disable protection on page"].''