It's rare that I have a problem with Firefox. But I can consistently make it fail when loading up a Java applet. I use the official Java distribution from Sun (version 5 with fix pack 6) to no avail. One particular applet that resides locally on my machine causes my browser to lock up instantly, every time. Perhaps the problem is with the applet itself. Or perhaps it's "just Java." But the applet works in (yuck) IE. Shouldn't Firefox yield the same results?
I have yet to poke around in Bugzilla to see if there are any bugs filed on this problem. I can't believe that I'm the only person who runs into this on a semi-regular basis. Granted, I do my best to avoid Java at all times. But every so often, I have to make use of this technology, regardless of my level of disdain.