Mozilla has released an add-on recovery tool for the recently released Firefox 7 for helping people who have missed their add-ons after upgrading their Firefox from the previous version. Though Mozilla is planning to release a small update (Firefox 7.0.1) to fix this bug, meantime you can use the official Add-on Recovery Tool to fix the issue.
Add-on Recovery Tool is a restartless add-on by Mozilla. Just install this add-on and restart your Firefox. All hidden add-ons will be visible and usable. Your tabs will also be restored and this tool will remove itself.
