relating to extensions are
Extensions and Themes
When you upgrade to a new version of Firefox all of your Extensions and Themes will be disabled until Firefox determines that either a) they are compatible with the new release or b) there are newer versions available that are compatible. This is because Firefox changes from release to release and as such the ways in which some extensions integrate changes, meaning there can be problems when running an older extension with a newer version of Firefox. If you find that your favorite Extension or Theme has not been updated to be compatible with this release of Firefox, write the author and encourage them to update it.
This automatic updating of Extensions and Themes does not apply to users of Firefox 0.8 or below who upgrade to Firefox 1.0 or a later version. Those Extensions will be disabled when 1.0.6 starts, and users will have to download and install 1.0.6 compatible versions manually.
To prevent the kind of problems we had with the 0.8 release (users were having the browser not start with "No XBL Binding for Browser" errors, and finding that their theme was broken), all of your extensions will be disabled when you move to 1.0 or later version. If you were using 0.9 or 1.0PR, when you first run 1.0.6, Firefox will try and connect to update.mozilla.org to look for newer, compatible versions of your Extensions, and if they are available it will download and install them. If you were using 0.8, you will have to find newer compatible versions yourself.