Blame view line number and blame commit don't line up with source (BB-8788)

See attached screenshot of the bottom of a source file; the line number spacing is slightly greater than the source line spacing. As you scroll down, the lines begin to be offset vertically from their corresponding line numbers.

Browser is Firefox 21.0 on Windows, default fonts and sizes, default zoom. Zooming in and out causes the text to go into and out of alignment arbitrarily.