Firefox 3.6 Beta 1 will be released some time this week, sooner rather than later, so it is time for you to start checking if your add-on is compatible, and update if necessary. The add-on review queues are normally very busy during update times, so you should follow these guidelines to make sure your add-on stays up to date and it doesn't have to wait too long for a review:
1) Visit https://developer.mozilla.org/en/Firefox_3.6_for_developers and read all about the changes that have been introduced in Firefox 3.6.
2) Stay up to date with Mozilla news and check http://www.mozilla.com/en-US/firefox/all-beta.html frequently for the beta 1 release. The current scheduled release date is Wednesday October 28th.
3) Test your add-on with the beta and see if there are any compatibility problems.
4) If the current version of your add-on doesn't show any compatibility issues, you don't need to upload a new version. Visit the Developer Hub: https://addons.mozilla.org/en-US/developers/ and edit the compatibility range in the latest version of your add-on (it's in the Versions and Files section). That's all it takes.
5) If you do need to update your add-on for 3.6, submit your update as soon as possible. There will be an update rush after the final release of 3.6, and it will probably take a while for the editor team to catch up. Once the beta is out, you'll be able to set your compatibility to 3.6b1. No big changes are expected between beta 1 and the final release, so you'll probably be able to update your compatibility to 3.6 later as specified in point 4.
Also, if you have binary components, some important changes have been made to the C API which might affect your add-ons. Make sure you build your add-on against the newest SDK, which is version 1.9.2.
Jorge - Add-ons Developer Relations Lead