This might be too much for you, but if it's looking too tight, note that there's also a Density menu at the bottom in the customisation screen that lets you widen the interface (including, presumably, the bars).

I have my density set to compact, changing it affects the vertical space of everything except the bookmarks and menu bars. They remain incredibly tight.

That sounds like something that shouldn't happen! Care reporting it to them? https://bugzilla.mozilla.org/