What is for you the "overlay method"? The override approach? If yes, this statement is totally wrong:
The opposite. Using this method you can't ignore the rules from the default theme, because you have to override rules you don't like or don't fit your necessities. As I said before, normally you don't have to change a lot of things in your theme, because you are only touching a small piece of code (for example the code for toolbar buttons), but if the default theme changes the technique the use for those buttons, of course you have to change things in your theme...It used to be we could just ignore this stuff in overlay themes
And what drives you to think that
??? Do you have a bug number for making Firefox be "more strict" to interpret CSS? Do you have a concrete example of this behavior?but ever since Firefox 4.0 came out the CSS has been more strict
And why should you
??? Again: you just have to override the rules that don't fit your necessities.have to include everything the default theme has in order to override the instructions