I'd been passing it over, because it didn't sound all that useful, and because I kind of assumed that getting it to work with whatever player would be a hassle. Then int came out with a new version of Deepest Sender (my usual LJ client, and another Mozilla extention) that fixed some bugs and added some nice features—and also added automatic song recognition through FoxyTunes (DS had an autodetection feature before, but it involved jumping through some hoops and installing WinAmp plugins, and I didn't care all that much). So I thought, "what the hell?" and gave it a try. It seems pretty nice: being able to just click "detect music" is cool, having the WinAmp controls right on the browser window is way more convenient than I thought it would be, and I haven't stumbled over any bugs yet.
Actually, it's a lot cleaner than DS, even though DS has been under development for longer. Probably because DS is primarily the work of one guy who only fixes things when he feels like it, while FoxyTunes seems to have a reasonably dedicated crew and some momentum. The new version of DS, incidentally, doesn't seem to fix the bugs that actually bothered me (link mangling and the linkification button not working—the latter seems to be a conflict with another extention or something, but I don't know which). C'est la vie.