Hi, I search on internet some said that mousebutton config in Firefox Linux about:config are not available, but when I tried, it’s actually available. May be you want to try about:config on Firefox and search for mousebutton.
For Chromium base browser, for now I’m still can’t find any information about it even in their docs.
Btw there an app name input-mapper. Maybe you want give it a try. Bellow are on how to install it on Fedora Linux: