Just a quick note for anybody who has the same problem I did … I’m using Mozilla 1.7.2 as my default web browser and Mozilla Thunderbird 0.7.3 as my default mail application … cool, no Microsoft! But whenever I clicked on ‘mailto’ links in web pages, Mozilla Mail (the built-in mail app for the browser) not Thunderbird would open. I didn’t really want to install Firefox, just to get a stand-alone browser (eventually, but not right now). So I searchy-searched on the interweb and came up with one whole hit that solved my problem. (The link may not work, it didn’t for me when I linked directly, so try this one, it should be the first hit.) The solution it gives — to access and edit the ‘about:config’ page — is ingenious, but not published anywhere in the literature that I could find. I would have thought that it was a common problem with people in my situation, but I guess not.