If your problem is with bad developers not following the standards then why is your solution to screw the users. Find a solution for the problem bad developers and greedy companies. Such a solution for preventing IE6 like cases is to remind Apple that users should be able to install alternative browsers.

I test my stuff in Firefox and Chrome, can't check Safari or Safari Beta so if you really want more support for Safari you need to ask Apple to sacrifice a bit of profit and give developers virtual machines or whatever web service to be able to test their code.

But if you are honest with yourself you know the exact reason why Firefox is not allowed to be an option on iOS and the answer is simple, profits and sure a company is obligated to max out profits.