Scrollbar Blindness
I have to pile onto the criticism of the hidden scroll bars, and other similar features (like the hidden buttons of PDF viewers now, such as in Chrome).  Discoverability is a problem.For anyone (cough, elderly parents) who aren't adept at discovering hidden features, these things can be utterly mind-boggling and frustrating.   Even I was stumped for a good minute the first time trying to print/save/download a PDF when that "feature" came out.I don't really need the small sliver of menu space in PDF view to be reclaimed -- and for what, a "clean" look?  Those are real and important functions I desire.  What I actually need is for news and blog sites to stop covering 1/4 of their vertical window space with hovering frames, ads, and banners asking me to subscribe.   Which, by the way, subsequently don't properly calculate into that now hidden scroll bar's movement and cause you to overshoot the displayable area when paging down.  End rant.