Mozilla has released an updated version, 7.0.1, of its Firefox browser. The new version fixes an occasional problem with version 7.0, released Tuesday, in which extensions previously installed by the user seemed to disappear. (Their settings are preserved, and the extensions can be recovered.) More details on this issue, and on a recovery work-around for version 7.0, are in the Release Notes and a post on the Add-Ons blog.
You can get the new version via the built-in update mechanism (Help / About Firefox), or you can download versions for all platforms (Mac OS X, Linux, and Windows) from the Firefox download page.
Update Friday, September 30, 22:19 EDT
Mozilla’s E-mail client, Thunderbird, has also been updated to version 7.0.1 to address this same add-on issue. More information is in the Release Notes. As with Firefox, you can get the new version using the built-in update mechanism, or you can get the installation package from the download page.