I am well aware that we all got 10 fingers unless you are mutants. Why use only one, right? Well, when comes to UI, the less is better for users. And it's less UI behavior consideration for developers. That's all.
Well, it actually did. Compare the Firefox 1 UI with current FF5 browser you will notice how much the UI has changes, simpler and cleaner, and the history-back buttons are gone.
I do not think those pictures show what you think they do.
I can clearly see the back button in all 3 UI pictures, including the one for Firefox 5. For that matter, I can see the back button in the Firefox 5 window I'm using to type this comment. I agree that Firefox 5's UI is simpler and cleaner than Firefox 1's and Netscape's, but I don't know where you got the idea that they'd eliminated the back button.
Obviously you didn't read my reply clearly. I said "the history-back button" (one of back buttons)is gone, that is the little down-arrow button when clicked it shows the history.
So you would remove the back button in web browsers, right?