As we work on removing the Advanced font sheet (Bug 422576), here are some screenshots to help visualize the UI.
One persistent problem is that the Fonts and Colors tabs must be the same height (so we must be mindful of introducing big empty spaces in the less-busy Colors tab) and the “Reset” button is literally shared between the tabs (in order to make the key loop work).
Current Appearance pane
Old ExtraFonts third-party pane
missing "Always use my fonts" and font preview; font change buttons and default size are separate, extra UI
Mockup for Bug 281770
2px wider; no bottom margin; no equivalent Colors mockup
hendy's v1.0 nib for Bug 422576
cramped bottom; no bottom margin
ardissone's tweak of hendy's v1.0 nib for Bug 422576
slightly-cramped bottom in Fonts (9px), extra space (36px) in Colors
ardissone's 17px tweak of hendy's v1.0 nib for Bug 422576
extra space (44px) in Colors