My mother gave me a very common portuguese name: João. You can translate it to 'John', 'Jean', 'Juan' (take your pick). The odd thing about my first name are the three consecutive vowels and the tilde character on top of the 'a'. I get all sorts of funny jokes from my anglo-saxon friends due to this personal oddity. Why is this relevant?
I have been working with Silverlight 4 for a web application (I'm essentally rewriting a big HTML SaaS application) and met a very strange behavior with Silverlight 4 when running on FireFox (and Chrome): I just could not write my name on a TextBox! This is a situation that has been reported by some users but, interestingly, it's not a very common complaint. Of course IE works OK with this.
When searching for a solution for this problem, I found a sample where this issue did not happen. After a bit of research I found the culprit: the "windowless" parameter on the HTML object element (my code had it while the sample did not). If you set this parameter to "true", FireFox will not compose the '~' and the 'a' to produce the dreaded 'ã', so beware!
This issue is irrelevant for english-speaking (and writing) users.