Many people tested on various machines and we reach the conclusion that E does something funky with firefox.
On the same machine under X, firefox has webgl disabled in E and enabled in KDE.
I personaly tested with E_X and Weston with firefox running under Xwayland and was not working in E while working in Weston.
Many other people confirmed it. EFL compiled with EGL might be a cause but at some point this was working with E.