If you've had the extensions disabled in Firefox 3, there is a way to get them going again.
After installing a beta of Firefox, typically all the extensions will fail and the user is prompted to check for an update.
However, not wanting to believe that I couldn't use Greasemonkey with Firefox 3 -- it turns out that there is a way to get your favourite extensions working again. And it is incredibly simple.
Following the instructions in this comment thread will get your extensions back.
To summarise the recipe:
- Download the xpi file, this is easiest in a browser other than Firefox
- Extract the xpi with your local unzip utility
- Open install.rdf with a text editor
- Rezip contents with your zip utilty
- Open file in Firefox
After that it is the standard install and restart procedure for extensions.
This technique works with Greasemonkey and Firebug extensions, but I'm sure that there are extensions that will fail and cause some chaos.
As with any beta hacking, YMMV.