Firefox requires that add-ons (extensions and themes) specify which versions of Firefox they work with. Some add-ons have yet to be updated to work with Firefox 3. After you upgrade to Firefox 3, if some add-ons are not marked as being compatible, Firefox will disable them.
Some common ones that have yet to be updated for Firefox 3:
Others have updates that you may have to get manually:
If you have one of these add-ons, you should contact the author of the add-on. They will have information on if and when an update will be available.
If your add-ons claim they are compatible with Firefox 3 but you're having problems installing or enabling them, see Unable to install add-ons.
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