I've been working on a client for Mozilla (looks and acts a lot like the Visions client), and got it up online at http://deepestsender.mozdev.org
Currently all it can do is post with most options and post to different journals, it can't edit friends or history or check if anyone's updated their LJ, but I'm working on it.
I've only been coding XUL stuff since last Friday, so I'm kind of a beginner - sorry that the source code looks like barf at the moment. I'll clean it up and everything as I go along.
It should work in both Mozilla 1.4 and Firebird 0.6.1. I don't know about older/newer versions but I can't see any reason why it'd die.