I switched to K-Meleon last year, after years with Firefox, because I got frustrated with Firefox 2 being painfully slow on my system, especially each time it had been running a few hours.
The main feature of K-Meleon is that it's incredibly fast. Amazingly fast, and yet still fully-featured. I loved it. Then Firefox 3 came out and it addressed most of the performance issues from FF2 and I was lured back by being able to have the functionality of my add-ons.
K-Meleon can run Mozilla/Netscape plugins but not Firefox add-ons, unless they've been specially adapted. It will run Java applets natively as long as JRE is installed. There's a little macro language which you can have a look at
here.