Start Firefox in <u>[[Safe Mode]]</u> to check if one of the extensions 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 If it does work in Safe-mode then disable all extensions and then try to find which is causing it by enabling one at a time until the problem reappears. * Use "Disable all add-ons" on the [[Safe mode]] start window to disable all extensions. * Close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit") In Firefox 4 you can use one of these to start in <u>[[Safe mode]]</u>: * Help > Restart with Add-ons Disabled * Hold down the Shift key while double clicking the Firefox desktop shortcut (Windows) ---- * https://support.mozilla.com/kb/Troubleshooting+extensions+and+themes

Install this add-on, then you won't be bothered by ads anymore: https://addons.mozilla.org/en-US/firefox/addon/adblock-plus/