I agree that the Acrobat plugin was a pain (and I always made sure to disable it in Firefox), but I absolutely love the Firefox in-browser PDF viewer. It doesn't lock up the PC while loading, and it has a convenient download button that doesn't seem to redownload the PDF when clicked (much like saving an already loaded image).
It might have something to do with my PC (i7 x220) but I cannot stand the Firefox viewer for anything but plain text. I find it very lacking in terms of performance compared to a native pdf viewer. Everytime a somewhat complex pdf opens up (mostly formulas, few images), the fan begins to rev up significantly..
Firefox's reader is an improvement over Adobe's, sure, but that's like beating snail in a foot race. Go Firefox, you show'em Chrome! It's still not SumatraPDF, it's not Evince. Saving the file and having it auto-open these programs takes less time then waiting for the browsers PDF readers to kick in. Of course it could be better, but frankly, I'd rather things be more unix'y, not less.
A major problem with saving all pdf files to be opened in a separate program is having to delete the temporary files afterwards. That's not very unix-y.
Another, less common, problem is erasing the URL in the process.
There are other readers in Windows (besides Window's 8 built in metro (full-screen) reader). Ever hear of Foxit http://www.foxitsoftware.com/Secure_PDF_Reader/ ? Mush much faster than Adobe Arobat.
