Get the goal of pixel perfection out of your mind. It can't be done, because you don't have a clue how each person's browser/system is configured. And it shouldn't be done, because then it's too easy to forget about graceful degradation.
That's ridiculous. You don't stop striving for perfection just because there's no such thing as absolutely perfect. Are you suggesting designers not develop pixel-by-pixel until the site looks like exactly what they want it to be in their minds? Yeah - that won't work for everybody. At the same time, that's no reason to stop designing as anally and as focused as possible. I hate that mindset: by that standard why design at all? Why not make everything black-on-white, no borders, no margins, just a list of features you can click on?
Either you design, or you don't design. There's no in-between. If you're designing something, you had better be designing with everything you've got, and yes: that means jiggling pixels until they look absolutely perfect. Apple does it, Facebook does it, I do it. Lots of designers do it. There's no reason for you not to do it.
For example, on account of my accessibility issues, Facebook looks like crap and its horizontal scroll bar is even defective. And, no, I'm not changing my configuration just to suit Facebook, or Google, or whatever.
With respect, are you complaining that because you changed your browser's interpretation of the web, something on another site broke? So now you're saying that because of the things that you changed on your computer, it's a fault with Facebook's design. Am I missing something here? Because that sounds pretty snotty.
If you've got accessibility issues, then you're going to see drawbacks when you're using things. Yes, that's the job of the designer to fix, but if they work on fixing it and it's not a completely perfect fix, that's not saying anything bad about their original design.
Sorry I'm so testy, but pixel perfection really hits my buttons.
It's okay. We've all got buttons that get pressed. Mine are pressed when people suggest that it's not worth aiming for perfection. Every great thing that's ever been made had people saying it wasn't worth trying.