Each MFD selects its own font when it renders, so the ability to configure a given MFD's font depends on whether that MFD's code supports that. I don't know of any MFDs that support configurable fonts, but it's possible that some MFDs, somewhere, do. You could check the documentation for each MFD that you're interested in updating.
If you primarily want to change the font size on all MFDs, you could play around with the "Panel Scale" setting in the Orbiter Launchpad: that will scale the size of all the 2D panels, though, not just the MFDs. But it's useful if you're playing on a high-resolution monitor and want to make the 2D panels fit the width of the screen. :tiphat:
Thanks for the response dbeachy. The panel fits the screen just fine, so I don't want to increase that. If I want to go with a panel that is larger than the screen I can just reduce the screen size and make the font bigger that way.
I've tinkered by removing the core fonts I installed in Wine (yeah, I know Orbiter is best on Windows). Whatever font Orbiter is pulling from my system it displays better than the courier it picks up from the core fonts. However, that creates other issues. The line spacing in the secondary hub is off because the typeface is taller. Also, strangely, Pursuit MFD gets all out of whack in its formatting if it can't find courier - more so than I'd expect from merely changing the font.
Unless I find another solution I'll probably just use the glass cockpit when the smaller panels give me too much grief.