When I go to RuneScape, I click play, I choose a world, and then when it loads, I just see a white screen. Nothing happens.
One hr ago I happily cooked my trout( to Maki) and then turned Firefox off. I click on it, type runescape.com in, click on play, chose my world, still a white screen. What is up? I have Java. I have it abled on RuneScape, it is chosen as my trusted website. What now?

What version of Java? How long did you wait? Did you alternate tabs?

Try turning your computer off and then back on. Sometimes FireFox.exe remains running in Task Manager even though you close the browser. Restarting will fix that as well as the "multiple machines are running" Sun Java error so it's worth a try.

Ok it is running now. TYVM anyway.