I just broke something
Everything else is fine. If I use the browser to visit another site, the text is normal size, but when I come back to Rpol, it's small font.
On my current screen, the browser menu headings (File, Edit, View, etc), the Forward Backward arrows and the address bar is all normal size, but everything within Rpol from the box frame logo down, is in small font.
...However, I just clicked the zoom in function, and it's back to normal. That must have been it, Nauthiz, but I never got near the zoom control unless there's a shortcut that I accidentally pressed somewhere near the keys for CTL+C or CTL+V.
Looks like the fact that the mouse was over 'small' at that exact time was just a confusing, coincidental, red herring.
Anyway, problem solved. Thanks both. :)