The initial configuration box is borderline unusable, it has a vertical scroll bar, and the buttons are likewise vertically huge. I can take more screenshots if needed, but I do not have system with an English version of Windows, nor easy access to anything that isn't Windows 10 at the moment.
Disabling the font whitelisting by clearing font.system.whitelist "resolved" the issue. This is utterly infuriating because with whitelisting disabled, Tor Browser is claiming to be using the fonts that were explcitly added to the whitelist as part of the change that broke this (Localized MS P Mincho/MS P Gothic).
A ha. After poking at it a bit while chatting with arthuredelstein on IRC, adding Yu Gothic UI to the pref fixes the problem. Per the interwebs, the default GUI font on windows has changed a few times on Japanese windows...
Windows XP -> MS UI Gothic (Not sure if this needs to be localized, don't have a box with this)