Walter, thanks so much for the feedback as sometimes things unexpectedly are impacted by modifications and break. But I don't think that is the case here. The variable is not $CIN_BROWSER, but just CIN_BROWSER without the $ in front. Although I have no other browsers to test, I did the following and got the following result:

[root@keystone bin]# CIN_BROWSER=firefox-developer-edition ./cin
Cinelerra Infinity - built: Jan 26 2021 09:26:19
...
/bin/bash: firefox-developer-edition: command not found

In addition. I used on the command line: CIN_BROWSER=vi ./cin

and vi did come up in the terminal window. And just to be sure, I tried it as an ordinary user instead of root with the same results.

yes, add the variable in .zshenv, because I use zsh, but beyond that it seems that cinelerra doesn't read the environment variables. because firefox is still