content: This is not entirely true. Pale Moon forked Gecko many months ago.  They called it Goanna. Firefox will still use "Gecko" but it will be a radically different engine after incorporating the Servo components (under the "Quantum" project). The real point of contention here is the Mozilla platform (aka the Mozilla Application Framework) of which Gecko is a major part.   It's this framework that provides all the power of XUL/XPCOM.    "Quantum Gecko" cannot be integrated into this platform.  Which is fine with Mozilla since they intend to abandon the platform anyway.  In some sense, Mozilla is forking their platform for use exclusively with Firefox and gutting it (removing XUL/XPCOM) in order to continue developing Quantum Gecko. This means that the Pale Moon team will have far fewer opportunities to benefit from upstream changes to Gecko and the Mozilla platform as the codebases will diverge in fundamental ways.