Shouldn’t use Firefox or Chromium in Whonix. Reasons, see:
Using Tor Browser in Whonix. Anonymity vs Pseudonymity, HTTPS Everywhere, Torbutton, Protection against dangerous JavaScript, NoScript, Tips, Update Tor Browser, Browser Plugins, Change Language
Shouldn’t currently use Debian Chromium package. Reason, see:
Debian version of Chromium reported to be exploited in the wild.
Patch Google Chrome with the latest updates – if you don’t, you’re vulnerable to a zero-day that is actively being exploited, the US Cybersecurity and Infrastructure Security Agency (CISA) has warned.
Criminals are targeting users of Chrome with outdated installations, CISA said in an advisory note urging folk to update their browsers immediately.
“Google has released Chrome version 86.0.4240.183 for Windows, Mac, and Linux a…
General notes:
^ Above page also contains instructions how to use Tor Browser or Whonix generally with a proxy (User → Tor → Proxy → Internet).
Tor Browser proxy settings also here:
Tor Browser Advanced Topics
Shouldn’t change time zone. Reasons:
Post-installation Security Advice
I can confirm what Whonix to my knowledge doesn’t contain any code to restrict proxy use (anywhere, in Firefox or Chromium). Certainly not intentionally.
Would probably be same issue on Debian without Whonix involved. Therefore suggested to resolve as per Self Support First Policy for Whonix .