I ran apropos browser in BASH and saw sensible-browser, so I ran sensible-browser and it opened a new page in my running browser (Opera).
I ran man sensible-browser
, and it told me to see the following for the environment variables:
It's not clear about where to set them, but the trail seems to lead to /etc/environment, which, in my system, is empty.
According to this link
, Debian does not use that file (see section 5.4).
My advice would be to let well enough alone.