No. Unfortunately above cannot be changed. It seems it is now hardocded in a binary file: /home/user/.tb/tor-browser/Browser/libxul.so
To make sure my method is valid of using user.js is right, that the file path to user.js is correct, that user.js is generally supported. Yes. Generally using user.js method is still functional. For example the following setting could be changed for testing purposes:
If you were to maintain 2 copies of the Tor Browser, then you could configure it in policies.json instead, which might yield different results. I’ve only done a little testing on my end to experiment with in-I2P TLS certificates, but so far this mechanism has allowed me to configure some things in Firefox which I could not before.