Did you tried to find out the actual name of your package that install
firefox. Some distros name it "mozilla-firefox" others "firefox".
Try apt-cache search firefox or dpkg -l firefox (I'm not sure of the
syntax of dpkg...I'm on gentoo now).

An other avenue would be to just wipe off your profile and restart
with a new profile. Just start the profile manager by typing "firefox
-ProfileManager &". And clean up the mess. But you'll have to
reinstall your extensions...

If you want to avoid that. You could search in your firefox hidden
directory to find out how the "windows live addon" is connected with
firefox... There is a "plugins" directory that may be of interest.

And last, but not least, just find out who is responsible for that add
on. There must be some support available on a support web site. (I
haven't found this add on with my plugin search)... So I can't help
any more.