Update 2: Never mind this. 7.6.9 has the updated viewer.
Update: found a reference on the linked reddit to a github issue which pointed out the connection problem has been fixed in 7.6, currently in beta. That's got to be a better idea than downloading an old version. Maybe by the time anyone reads this, the beta will even have been updated to show GPU-core proteins correctly.
Thanks for the old version tips. I was able to get the viewer working on Windows by...
0) Making an entry for "C:\Program Files (x86)\FAHClient\FAHViewer.exe" in Windows Firewall (as stated above, probably necessary, but not sufficient)
1) downloading the beta from
https://foldingathome.org/beta/ (old: Googling for a download for Folding at home 7.4)
2) Opening (don't have to run) that .exe installer with 7-zip
3) Copying just the FAHViewer.exe (replaces) (old: and freetype6.dll (new file)) to C:\Program Files (x86)\FAHClient