This ticket keeps track of the proposed way to access localhost daemons with TBB and redirecting darkweb TLDs (.i2p) with privoxy. This is a more superior approach than running foxyproxy which cannot be installed by default, needs updates to its rule lists to support new things, opens unsafe ads for their aid service and breaks for no reason all the time.
https://forums.whonix.org/t/tbb-profile-with-custom-about-config-settings/4888/4
You can create directories in tor-browser_en-US/Browser/TorBrowser/Data/Browser/ called (profile_name).default. Here will be all the configurations for the profile. It should have a custom user.js with proxy settings using privoxy and setting network.proxy.no_proxies_on to 0.
In tor-browser_en-US/Browser/TorBrowser/Data/Browser/profiles.ini you would add the new profile so Tor Browser can use it.
For example, if the profile is called "privoxy" then you would add:
[Profile1] Name=privoxy IsRelative=1 Path=privoxy.default Default=0
This profile can then be started with tor-browser_en-US/Browser/firefox.real --profile=(path). You can add this command in start menus, desktop icons etc.