I’m using Firefox 2.0.0.4 and Thunderbird 2.0.0.4, both with default themes on Win XP SP2, and recently the “File-Send Link” function stopped working. I checked the forums and found out that this was a problem with the Beta release but can’t find any info on later problems or issues. I’ve checked both programs for updates.
Any advice out there? No, I don’t need advice to switch to Linux or to Mac, as I plan to leave Windows completely next year. For now, XP suits me fine.

Have you seen this?
http://groups.google.com/group/Firefox-Users/browse_thread/thread/8706b150646a34b0
Look at that key in your registry and see what it says.. The mailto one.
It would be an idea to turn off extensions and see if it resolves it, then turn them back on one by one. I had to get rid of the Developer toolbar because it had become a real nuisance.
One last comment before I take off to work: http://kb.mozillazine.org/Problematic_extensions
Look especially at the Google Toolbar entry
Thanks, Gerard. The last link helped me out. I had to change the about:config setting for my external mail handler – how obvious ;-)
about:config, THAT’s what I was trying to find originally..
Glad it worked. :)