Delete the files extensions.* (extensions.rdf, extensions.cache, extensions.ini, extensions.sqlite) and compatibility.ini in the Firefox [[Profiles|profile folder]] to reset the extensions registry. New files will be created when required. See "Corrupt extension files": http://kb.mozillazine.org/Unable_to_install_themes_or_extensions If you see disabled, not compatible, extensions in "Tools > Add-ons > Extensions" then click the "Find Updates" button (in Firefox 4: right-click the extension -> "Find Updates") to do a compatibility check. ---- Your above posted system details show outdated plugin(s) with known security and stability risks that you should update. # Shockwave Flash 10.0 r45 # Next Generation Java Plug-in 1.6.0_15 for Mozilla browsers Update the [[Java]] plugin to the latest version. *http://www.oracle.com/technetwork/java/javase/downloads/index.html (Java Platform: Download JRE) Update the [[Managing the Flash plugin|Flash]] plugin to the latest version. *http://www.adobe.com/software/flash/about/