Worthy side discussion from Compatiblity Thread

[Antonius32]

In listed version is a that theoretically supports Pale Moon. Have you tested?

Yes, I have, just now - but I prefer version 2.3, because it has the "Smart Popups" feature, so you don't lose the window control buttons on pop-up windows. If you don't care for this feature though, I think you might as well go with a newer version.

[Moonchild]

Name: HTML5 Video Everywhere
Type: Add-on
Issue: There is no version listed as compatible
Cause: Minimum supported Firefox version is 0.26
Workaround: n/a
AMO: https://addons.mozilla.org/firefox/addon/html5-video-everywhere/

There is ticket on bug tracker that states Palemoon won't be supported until it has more HTML5 features.
https://github.com/lejenome/html5-video-everywhere/issues/60

Why even report it here if it was never compatible? We can't possibly start rewriting extensions that were never written for a compatible code base.