hello
firefox 49.0.2 dont support Bitcomet add on , please fix this problem .
thanks for all 
.
Try installing FlashGot extension, it will allow you to integrate multiple download managers including BitComet.
Bitcomet’s extension used to be based on flashgot, not sure if it still is, but the people at mozilla started disabling all extensions every time they update the browser, in effect forcing all the publishers to replace their products at mozilla’s timetable which caused many freeware apps to stop supporting firefox. BitComet’s development team has never made any public statements on this subject, but it’s pretty clear from their actions that they aren’t willing to update their product every time mozilla disables their extension, so the only options are either use another browser, or don’t update firefox until it’s supported by bitcomet, or use the flashgot extension instead.
Personally I stopped using firefox for this and other reasons, but even before I switched to google chrome, I had always used flashgot instead of the bitcomet extension. It allowed me to select how I wanted to handle each download.