I am currently having problems connecting to the music streams from sirius.ca, using Firefox 13.0.1 and gnome-mplayer 1.6.0-2 on Fedora 17 x64. I get the error message that a file is not found, ~/.cache/gnome-player/plugin/gecko-mediaplayerrevwyk. The last 6 letters vary but the rest is the same. I checked and indeed there are no files in that directory.
I tried the same exercise with a Gentoo system I have with slightly older software .. Firefox 13.0 and gnome-mplayer 1.6.0, and it works, and the files do appear in the plugin directory.
Back on Fedora 17, I tried substituting the Totem plugin for the gnome-mplayer one, and it simply crashed on a segmentation error when I tried to connect to the stream.
Note that Sirius.ca has a userid and password associated with the stream request, and this probably complicates things.
I can listen to Sirius on Fedora using the application pyxis, so the problem does seem to be with either Fedora or gnome-mplayer or perhaps both, but not with mplayer which pyxis uses.