Ran FD again. It found a couple of duplicates (none of which would be associated with a website), which I moved. Plus I emptied the font caches. Did this on both machines. The MBP only displays the garbled text in the log-out link at the top right, but the text below the icons is ok. On the Mini, all text except my name is garbled.

Safe mode clears it out, but another restart screws up the text all over again. So I'm convinced this has more to do with Safari than anything else.