A few settings you may wish to consider for your firefox’s about:config page.
browser.ml.chat.enabled = false
browser.ml.chat.shortcuts = false
browser.ml.chat.shortcuts.custom = false
browser.ml.chat.sidebar = false
browser.ml.enable = false
browser.tabs.groups.smart.enabled = false
There used to be an admx, we’re using it (to enable Firefox to use system cert store and the like). I hope it’s updated quickly after new releases, but I never had an urgent need for that until now. Guess I’m also finding this out on Monday…
I found this, but I’m still working out the oma-uri stuff. Very much not my forte, but maybe this will help you.