Development problem solved

I was finding that new versions of the code were not being acknowledged in Firefox, so that even if I made a change, it kept the old code.

Discovered that you have to bring up the Java console and type x to clear the classloader cache. At first, IE didn't seem to have the same problem, but that was probably because I restarted IE every time I tested it.

Anyway, to be on the safe side, I clear the classloader cache every time now.

And using mousePressed() instead of mouseClicked() works a treat. The mouse response is very much better now.