Beware of the young birds before using them. As Robert reports, the current Firefox 1.5 Beta1 disables any extensions upon installing. There is no warning on the Firefox Website about that nasty glitch. I noticed some difference while updating from the last stable release to the Beta 1 but haven’t thought much about it - now I know.

Perhaps it depends on the version you’ve been using before, and as far as I guess, Robert was using a german-language variant of Firefox 1.0.6 - not sure how that reacts with the english version tho! However, there seems to be a workaround:

In the address bar type about:config
In the Filter line type: app.extensions.version
Now you should have a single line in the preferences saying app.extensions.version. If it does not exist just right click on the empty list and select New->String to create one
Now double click the value and set the value to 1.0 (from 1.5)

Note this is just a temporary solution and some extensions might crash Firefox - so be careful with this solution.