Bug 40054: Fix Circuit Display Spacing

This fixes the overlap I was seeing in the circuit display (when layout.css.devPixelsPerPx = 2)

The deeper issue here is that the UI fonts do not scale with layout.css.devPixelsPerPx on restart. EG if you start at 1, and change to 2, the fonts double in size. But on next launch, the fonts are all the original size, but the rest of the UI is scaled. I'm not sure what is causing this to happen yet.

EDIT: The cause of this is that (on Linux at least) UI/chrome fonts are set to be the same size as the desktop environment. This causes some things in the UX to break when elements are measured, positioned, scaled, etc in both pixels-based units and em-based units. The pixel-based measurements will be scaled by the devPixelsPerPx setting, but the em units are not. So, things which look correct w/o scaling may be misaligned/scaled/etc when scaling is enabled. This problem is kind of endemic to Firefox as a whole, so it's not just us screwing up here.

Fixes #40054 (closed)