Torbutton as a standalone extension is going away (legacy/trac#10760) and while doing so we restructure our toolbar making it more usable by exposing New Identity directly on it (legacy/trac#27511). However, we need to find a new home for the bridge configuration as well if we want to remove the onion button from the toolbar. The current plan is to move it to `about:preferences` as a general setting. This ticket tracks that work.