"Personally I am against anything to violates the operating system's UI design philosophy. And removing the focus rectangle certainly qualifies."
It only qualifies when the focus rectangle works properly. Half the time, Firefox puts the dotted outline right down through the middle of the button graphic, and it looks terrible. Plus, Firefox is hardly using the UI controls of the OS to begin with, so saying this has anything to do with the OS's UI is already laughable. Having a focus rectangle that doesn't look right doesn't do anything to improve usability.
We should have the ability to replace the native focus rectangle with one that actually works for our individual purposes, just as we should have the responsibility to of course replace the built-in focus rectangle with something similar so the user retains the same usability.
I'm so tired of browser makers (and developers!) acting like their way is the only way, and if you don't like it, too bad. Why not make things more open so that we have more options, and can craft the user experience that we want, as opposed to having to fit something into your rigid patterns of thinking because a few bad apples might not do the right thing? It's collective design censorship and it doesn't make any sense. If your site looks like crap or isn't usable because you're not putting the effort in to make sure it's a sound design, that's your problem. I don't need the Mozilla dev team to ensure that my designs make sense, I am perfectly capable of making that call on my own.