WebDeveloper add-on for Firefox 3.* (all betas and stuff)
Update: Web Developer addon now officially supports Firefox 3. Check out history (version 1.1.5). Download the new version here.
Old post about my hack:
Just a note that there are a number of features that do not work correctly in Firefox 3. I am working on fixing these and putting together a new release. You are free to use this hacked version of course, but just a word of warning.
Today I tried out the brand new Firefox 3 Beta 2. Nice. I like the new address bar and the ability to resume downloads after closing Firefox. The only thing I needed was WebDeveloper add-on (extension), which, unfortunately, does not work in FF3 yet. So, since I had a bit of add-on development experience I decided to change the max version inside the add-on. No problems occurred. Grab the .xpi (change file extension from "jpg" to "xpi" and open it with FF): 
That is all 