I ran across a weblog where user's with an AIM account have a AIM icon with the URL "aim:goim?screenname=Khym+Chanur&message=Hi.+Are+you+there?". I assume that this works with IE, and there should be some way to make it work with Mozilla, regardless of platform. I'm guessing that this would be tied in with helper apps, but I'm not sure...
Have you ever tried "protozilla" (http://mozdev.org). There you can specify any protocol type and configure very flexible how to handle them. I don't know if i want to have this in my plain mozilla, though.
16 years ago
there is a way to add Necko protocol handlers, if somebody really wants to get this working without hacking helper apps. Future-ing.
See bug 33282 for Linux. On Windows and MacOS there is an OS panel to set such bindings; if you tell your OS what app does aim: urls, we will use that app. aim: is not handled by IE, but is handled by Netscape, internally (using the Netscape AIM client). *** This bug has been marked as a duplicate of 33282 ***
-> networking VERIFIED/dupe: Basically, non-UNIX (Win+Mac) have OS level services for this. Linux does not, hence the dupe.