I overheard a developer looking for 15 minutes to find the "inspect" option when it became a flashlight. Now it's some square with a cursor pointed at it (which isn't so bad), but now there's a little "Off" button over on the right side instead of the way I typically closed the window. So now I double-take whenever I'm trying to hide Firebug-- I keep wondering for a split second if I'm clicking the right button.
I love Firebug more than any other extension ever (besides the Tree-style tabs), but the UI refactoring keeps messing me up.
1) Uninstall Firebug 1.4.0.
2) Go to the URL "about:config".
3) Right-click on the list of preferences and select New -> Boolean.
4) Enter the name "extensions.checkCompatibility".
5) Set its value to false.
At that point you can install the old version of your choice from https://addons.mozilla.org/en-US/firefox/addons/versions/184....I downgraded more or less immediately after 1.4.0 came out. 1.3.3 seems to work just fine with Firefox 3.5.
The icon was changed to the flat "box" design at the last minute as part of a larger icon re-design effort, and that happened when it did just because a volunteer showed up at that time to do it.