Still works in 3.7 Alpha!! Rated 3 out of 5 stars
I've just downloaded Firefox 3.7 alpha 5 (soon to-be Firefox 4), used my old profile, with Thinger and search bars installed, and surprise: IT WORKS. Search bars are fully functional. So we'll be able to use multiple search bars in this future version of Firefox, with this very old extension that no one seems to bother to update. Regarding this, specifically, I've got no thanks for the developers of Thinger or Firefox, they simply don´t bother to implement such a simple and essential feature of having more than one search bar; but I've got tons of thanks to the indefinite, chaotic and random reasons, amidst thousands of lines of Firefox code, that allow this old extension to continue to work! Thanks to that and nothing else.