At least the last three Firefox updates have corrupted the operation of the language bar on my full updated XP desktop.
After each of at least the last three Firefox updates (I was gone in the month of May and thus may be unaware of other updates), the language bar will not perform properly. Microsoft Word accepts Japanese entry correctly, but in Firefox it does not operate properly, specifically: once the language option is set to "Japanese," with input specified to be via hiragana, when I enter text it appears in unhighlighted Latin letters and neither offers kanji suggestions nor allows kana input.
My machine is a fully updated Windows XP machine. This problem always appears immediately after a Firefox update.
I've called the big guys to help you. Good luck.