There are people that customize Firefox with plugins to make it look like TorBundle. All you need is FoxyProxy[0] hooked up to tor and a useragent spoofer which mimics common TorBundle useragent strings and you're set. This is very dangerous though as FoxyProxy could potentially leak your IP, aswell as a slew of other things that could go wrong.
TorBundle devs have stripped out a tonne of things which increase attack surfaces and the fingerprintability of mainline Firefox. Best just blending in and looking like everyone else and use TorBundle.
Not only that, using the particular setup you're describing, you wont have stream isolation, so all of your website browsing can be watched by a single exit node (whereas with the Tor Browser each site has its own circuit) which makes correlation attacks much damaging (whole browsing history in a session vs 1 site).
TorBundle devs have stripped out a tonne of things which increase attack surfaces and the fingerprintability of mainline Firefox. Best just blending in and looking like everyone else and use TorBundle.
[0]: https://addons.mozilla.org/en-US/firefox/addon/foxyproxy-sta...