Hmm, you're right - I should have done more cross-browser testing. It does work fine in the latest Chrome, Opera, Safari, and IE 8+.
Unfortunately, I haven't worked with Firefox enough to be able to figure out what the problem is. I'll keep looking into it, but if anybody can figure this out, I will be much indebted to them.
This is cool! But the command line is pretty inoperative in FF (11.0 mac). I tried to take a look at it but it's not throwing any useful errors. I did notice that you are using jquery-terminal version 0.4.7 and there is a more recent 0.4.11 so you could try that? If that doesn't fix it, I will try and get it running on my local box to add some debugging and investigate asap.
Unfortunately, I haven't worked with Firefox enough to be able to figure out what the problem is. I'll keep looking into it, but if anybody can figure this out, I will be much indebted to them.