Yesterday, I made a few updates to the Firefox Profile Tutorial here at this website. It turns out that the -P command line option is case-sensitive (as it should be). Firefox 2 apparently doesn't care about case, but the new Firefox 3 builds do.

All of the official documentation I read also mentions the -ProfileManager command line option. I'm not certain if Firefox 3 wants the camel-case, but I've updated the tutorial to reflect this information. Let me know if you see any other errors in the tutorial.