I'm pretty sure there used to be contiguous white space between the body and, say, the activated Article tab (see screenshot). Now there's a line, and it makes me sad.
This is definitely caused by the zoom level, and, sadly, I don't think there's much we can do. I think Firefox does its best to approximate and that's that. Zooming out to -2 from default reproes the screenshot you attached, for me. IMO, you should close this as wontfix, but I'll let you make the call.
I'm not going to WONTFIX this, because yes, if you deviate too far from the default zoom level, Firefox compensates as best it can (similarly, try zooming in). But let's leave it for a contributor with some CSS mojo or a new hire. Really not important.
Priority: P3 → P5
Whiteboard: [good first bug]
Target Milestone: 2.7 → Future
now we have new design for https://support.mozilla.org
Status: NEW → RESOLVED
Last Resolved: 4 years ago
Resolution: --- → WONTFIX
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