How about LibreWolf?

As there seems to have been recent confusion about this, just a quick “official” toot to then pin: we haven’t and won’t support “generative AI” related stuff in LibreWolf. If you see some features like that (like Perplexity search recently, or the link preview feature now) it is solely because it “slipped through”. As soon as we become aware of something like this / it gets reported to us, we will remove/disable it ASAP.

https://chaos.social/@librewolf/115716906957137196

about:config is also available on stable release of Firefox.

You can access

chrome://geckoview/content/config.xhtml

and toggle

general.aboutConfig.enable

to ‘true’.