Many data. They even take measurements of how many seconds behind/fast your system clock is. Who knows what else they’re taking. You may look in about:config all pref with “clock” words. When browser never connect to firefox.settings.services.mozilla.com, there is only 3 prefs. The fourth (with data in seconds) is being created after first remote connection to they service. Sorry I`m lost site url with full list.
Ok. Little more research. Patch work fine if clean startupCache directory after aplying. Or just delete this directory and create empty file with name “startupCache”. Nothing change in Tor Browser work.
Developers should definitely implement it.