I really miss Chrome's multi-profile support, but it's just so much heavier. Last time I used Firefox (admittedly ~3 years ago) it was even worse. System-wide beachballs. Much worse than having Eclipse open. That's what got me to switch to Chrome for a time, after being a FF user since the Phoenix/Firebird days.
Apple also owns the app store and the default configuration of the OS is moving towards only allowing app store software (has it already finished that transition)?
They can and will reject anyone who uses private apis that they themselves use.
In addition, because they own the OS they can require that a private API is only accessed by software signed by them.
It also could cause firefox to break on OS updates and would require firefox to keep abrest of those changes.
Here's a couple references:
Apple does use private APIs: http://www.wired.com/2008/02/firefox_developer_uncovers_appl...
Apple rejected firefox from the app store at some point for using private apis:
That's not surprising, considering it's the only product not forced to use the public web view object in iOS. It's like Microsoft Office, which has always used private MS apis that other products running on Windows were not allowed/supposed to.