Rated 5 out of 5 stars
It seems to be intentionally making the addons bar visible and moving itself back there after I move the button to the tabs bar and untick the addons bar :(
Would the code at http://mike.kaply.com/2011/01/25/the-firefox-4-add-on-bar-for-developers/ prevent that?
This is a great addon to point people to that keep pestering us on IRC about "when will Firefox 4 come out?"
Yup, this extension exposed multiple bugs, and two of them are matching what you described:
Would love to see them patched :)