Firefox's popup blocker is enabled by default. Are there specific settings/tweaks you want to add? Whoops, I saw "Set" but didn't see "off" -- the below information is still what you want to look at.

Firefox supports an Autoconfig file in the program folder which can pre-set or lock preferences in individual user profiles. For more information, this blog is very useful:

https://mike.kaply.com/2012/03/16/customizing-firefox-autoconfig-files/

You would have to place these lines in mozilla.cfg:

// mozilla.cfg needs to start with a comment line
lockPref("dom.disable_open_during_load", false);

See also Configuration:

• https://developer.mozilla.org/en-US/Firefox/Enterprise_deployment