Ff 3. .....

just finsihed javascript game, works np on IE 6 and FF 2.0.0.17
does not work on

Mozilla/5.0 (Windows; U; Windows NT 5.1; sl; rv:1.9.0.3) Gecko/2008092417 Firefox/3.0.3

at all !!!

nothing in javascript console.

Is there any hope that if I install ff3 that it is backward compatible ?

Most likely that's because they fixed some quirk or bug that you relied on. May we see the code in question?

sorry, my own bug, the kind that comes out only in one of 1000 tests.
Nothing wrong with FF3 there.