I’ve been trying the newest Firefox betas for some time and I love its incredible speed and cleaner looks, but not having my extensions with me because they were incompatible with FF3 was a showstopper for me. Now however I have found a workaround:

extensions.checkCompatibility

With this value set to true in the about:config screen you can use extensions on FF3 that have not yet been enabled like the awesome Gmail Manager, All in one Sidebar and Download Statusbar. Be careful though that these have not been tested and you’ll probably run into some problems (like I did with FireBug).
If I conviced you to try Firefox 3 then there’s a super easy way to install it with one command: