After editing an answer to shorten long lines to remove large horizontal scroll bars I noticed that the largest codeblock had about 2 pixels of vertical scroll in Firefox which looked really sloppy. I then compared across the other browsers on my system. Chrome didn't have a vertical scrollbar but put a horizontal one of a few pixels on the 2nd code block. Edge and IE have scroll both of the scroll bars.
I can't easily tell what's going on vertically, but in the 2nd code block FF is rendering the text slightly narrower than the other browsers are.
Is this a case of browsers still not quite rendering html identically, or is SO's layout glitching somehow?
If OS also turns out to matter, I'm running win10 v1511.