I could be totally wrong here but just hazarding a guess, it might be worth checking that your Flash Player is up to date... latest version is 11.3.300.265. (If you need to download this from the Adobe site make sure you uncheck the Mcaffee download tick box.. otherwise you'll get that too...)
FF v13 does have some incompatibility issues with Adobe Flash Player and Java. FF v13.0.1 was supposed to sort these out but my experience, is that there a still a few problems to be addressed...
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