When I open Firefox, the browser does not open. Instead I get a small window that says: TypeError: Components.classes[cid] is undefined. How do I fix this?

Start Firefox in <u>[[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.com/kb/Safe+Mode *https://support.mozilla.com/kb/Troubleshooting+extensions+and+themes

Possibly you have "AVG Safe search" extension installed as part of "AVG Free", solution involves reinstalling :AVG Free" without the Link Scanner component see * http://kb.mozillazine.org/Problematic_extensions * symptom was noted in https://support.mozilla.com/questions/865877 Other possibilities * "OneClick YouTube Downloader 1.07" as reported in *: https://support.mozilla.com/questions/864343 * "Java console" needs to be updated as reported in *:https://support.mozilla.com/questions/863711] * "HP Smart Print 1.0" as reported in *: https://support.mozilla.com/questions/857283 * "McAfee Site Advisor" as noted in (also see Problematic extensions above) *:https://support.mozilla.com/questions/802381 *a theme After switching to the default theme the JavaScript error doesn't appear. (View > Page Style > No Style or if "Firefox" button use "Alt" first to get to the View menu) *:https://support.mozilla.com/questions/837840 *various extensions/applications but is 1 year back and Firefox 3.6.6 *:https://support.mozilla.com/questions/729606 If none of the above solve you problem use diagnostic approach... *: https://support.mozilla.com/questions/837840