So two things. The MSI installer will convert a local (EXE) installation to a global install (updating shortcuts and removing the local profile install whilst preserving the chrome profile).

Second, Firefox does have ADMX policies (ADMX being used primarily after Vista): https://github.com/mozilla/policy-templates. I believe it took them so long because they were initially reluctant, user freedom etc. But I guess Chrome's success in enterprise made them reconsider. Honestly I never considered Firefox for our Windows Domain because of the lack of Group Policy support. Now I deploy both and users have options :)