thats a really bad news, as for me QSB was the best extension for firefox I've seen so far. Intelligent and simple to use, actually i dont understand why this behaviour isn't standard in all browsers.
Have you tried changing your addon concept? instead to modify the FF search field, make your own input which can be placed in the toolbar. I havent developed a FF Addon so far, but I think that could be a good way to minimize changes needed to be made when a new FF version comes out, because the only thing you need from FF is its search engine database, which won't change as often as the UI does...
option 2: get some other developers on board to reduce your workload!
think about it and make your fans happy again ;-)
PS: sorry for spamming in this addon's comments