rmd hacks
First things first. I’m about to describe a workaround for the remember mismatched domains Linux problem for Ubuntu users but I want to be clear that this is a hack and a “you’re on your own” modification. I’ve been using it on my Firefox install for a little while now with no significant problems but your mileage may vary. Being Linux users I figure you (we) are probably used to living on the edge. With that disclaimer out of the way, onto the workaround…
As I described in the report for the bug that is responsible for the Linux problem, deleting the compreg.dat file in the Firefox (or Thunderbird) profile directory will cause all XPCOM components to be re-registered when FF / TB is launched. And as others have discovered, the first time RMD’s component is registered everything will work perfectly. You’re probably already jumping ahead of me now, but the workaround I’m using is to delete compreg.dat each time Firefox is launched. I’ve done that by adding the following lines to the firefox shell script (/usr/lib/mozilla-firefox/firefox):
#RMD hack - forces re-registration of xpcom components
rm ${HOME}/.mozilla/firefox/qy06zi95.default/compreg.dat
Of course your Firefox profile will be in a different directory than mine so you’ll need to modify appropriately.

Like I said, its a hack.