Sorry to be confusing. I meant I use firefox on my laptop to convert flv files to a format that will "work" on my N900.
If I understand correctly, the flv's aren't working on my N900 because the codec is the wrong type?
Anyway I tried the extra decoders support...when that didn't "work" I tried some "code". Then removed it. Later I read that you need to overclock and other stuff...

My simple "firefox" strategy sometimes fails like Copernicus discussed. I have another program "Hamster Free video converter" that I sometimes have to run the file through before firefox will convert it.

I'll take a look at ffmpeg...Here's a windows version I found.