A very good test of a multi-item interface is to imagine it with exactly TWO items and see if it makes perfect sense that way. Or if it’s a toggle button, look at a single button and see if you know its state.

Now in this context, imagine the inactive item is invisible and clickable, and the active item looks like a button (that is traditionally clickable) but is not clickable. Imagine furthermore that you still have freaking buttons elsewhere in the same UI that look the same as the unclickable thing but are clickable, well, you have a problem. Now imagine the even bigger problem of reusing the exact same style for things like text fields that have an entirely different function.

This isn’t just Firefox, a lot of this is what Safari tried to pull, too. Or the entire concept of flat UIs.

I really, really want to respect the field of UI design and imagine that this stuff is hard, etc. but frankly some of this stuff is really not that hard to get right. There needs to be discipline, some science, some user testing, and someone with enough power to shoot down the truly dumb decisions, for a start.

And barring all that, I want a config file (or back in the day, ResEdit) where I can undo all the madness.