If you are using FireFox 4, I thought I would quickly remind you to update to the release candidate if you have not already done so. Keep in mind that although its out of beta there may still be some bugs.
If you have not already updated FireFox 4, click the firefox button > Help > About FireFox.
Once you click that Firefox will check for an update, if an update is ready just click install. As you can see from the screenshot I am on the RC.
Most add-ons should work just fine, as many have now been updated to support Firefox 4.
After you have updated FireFox you may also want to update the add-ons.
Click the Firefox button> Add-ons > Extensions
Once you are there click the little settings button > Check for Updates.
If there are updates, click on “View Available updates” and click install. This should also check for any updates to any themes as well.