Jaws and NVDA have keystrokes (jaws/nvda + f, and there are others) for reading format information. This does help with CSS if you've gotten something wrong and it resorts to the default, but if there's a case where the error isn't ignored but doesn't display right either, they'd just read the mistaken version and you'd still be lost.
There have also been issues with certain screen reader / browser combinations not reading format information correctly, but I don't know the specifics, or if all of those have been solved, or what.
NVDA doesn't do screen review well with Firefox, but some layout information might be easier to follow by using a screen review or Jaws cursor type method. Maybe even use a touch screen, if possible, but since most elements are very small, that might be more trouble than it's worth.
Hopefully this helped in some way. If you're using Jaws, there are more advanced ways to get style information, but I don't remember them off hand.
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