The method will not change, it is a requirement for Vista compatibility and is set in stone by Microsoft. This issue was a blocker for Firefox 2.0 but a fix did not land in time and the blocking status was removed. I will say 2.1 will be Vista compatible.
You can read up about the new requirements for Vista here:
http://msdn2.microsoft.com/en-US/library/aa969375.aspxand here:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnlong/html/AppComp.aspGoto the "Default Programs" section.
Note currently Mirc does not get the correct default browser on Vista regardless. With older versions, Mirc will use Firefox even if IE is set as the default browser. Which is as wrong as using IE when Firefox 3.x is set as default.
Another note is the reflow branch landed a week ago, Firefox trunk now passes acid 2 test perfectly, why use anything else
Honestly IMHO, the fact 2.0 does not work correctly is because 2.0 is not compatible with Vista. You should not support it under the Vista environment. You can not write code to work out if older Firefox's or IE are the default browser, as the two coexist without conflict with the mismatch in settings(hence why both say they are the default). Trying to write a work around for a browser that just simply does not work on Vista seems pointless. The method I have described has nothing to do with IE, firefox or other, it just is how the default browser is set on Vista.
