All of those are very unlikely to be caused by Unity. The web player certainly does not mess up with Firefox’ tab settings, Caps lock state or Firefox shortcuts. Maybe he installed something else or did something strange to his machine, that just temporally coincided with web player install?
Anyway, I remark Internet Explorer is stabler (? I don’t if it’s a correct word) than Firefox, which crash always when I close Firefox and now and then when I play.