I love and use both Firefox-Dynasty & Chromium Legacy.
As for Chromium Legacy I'm now using version 120 (I was very happy with 124).
I tested some Firefox-Dynasty versions in different MacOS versions from 10.8 Mountain Lion to 10.14 Mojave, I'll share my results:
Firefox-Dynasty 128 versions works in MacOS from 10.8 to 10.14
Firefox-Dynasty 129.0.1 works in MacOS from 10.8 to 10.9 and 10.14
Firefox-Dynasty 130.0.1 works in MacOS from 10.8 to 10.9 and 10.14
Firefox-Dynasty 131.0.1 works in MacOS from 10.8 to 10.9 and 10.14
Firefox-Dynasty 132 works in MacOS from 10.8 to 10.9 and from 10.12 to 10.14
Firefox-Dynasty initially crashed because I used Firefox profile selector, I needed to turn it off "Set as default profile" with url about: profiles.
Edited to remove the emoticon from about: profiles
Just tested to be able to navigate various sites, didn't test DRM. Tested in actual MacOS versions not virtual.