I use firefox 4 form beta 9 to RC (zh) now and there are also firefox 3.6 installed in computer. One day when I open Fx 4 RC, some (actually a lot but not all) of the adoons just disappear. When I check on about:addons page, some addons installed do not appear in the list. The addons '''REMAINED''' including: * addons I already used in Fx 3.6 (like webmail notifie , xmarks) * ''addons only can use in Fx 4'' (like Open Web Apps for Firefox). The addons '''DISAPPEARED''' including: * addons I already used in Fx 3.6 (like yoono) * '' addons installed when using Fx 4'' (like updatescanner, Thumbnail Zoom). But when I check the profile(by Help > Troubleshooting Information>Open Containing Folder) , some (not sure is it all) of the missing addons related files are still here [lucky], so any one know how to make the missing addons back? Some more details: * This happened when i use RC for already a few days and keep on even i restart Fx and windows. * The bookmarks, history, search engine and even themes and icon setting are still here. [ I only sync bookmarks but not history for both xmarks and firefox sync.] * This addons are really '''disappeared''' but not disable only! * This number of addons missed, as i remember, at least 30, should be more than that number bacause some of them are installed but in disable mode. * I try to install back one of the addons - Stylish, the installed code are still here. * It is nearly an impossible mission to install every missing addons again, as it really kill my time.