I have a browser extension that works on Firefox 3.x but doesn't work with the current level of Firefox. The extension handles a new, non-standard, MIME type. The problem seems to be that at installation the process that handles the association between the add-on and the MIME type is not working. The existing code uses routines written in C++ as well as the usual XUL stuff. If you need a demonstration of the code before bidding please contact me.