The real strength of Firefox vs Chrome is in FF's real (as in not android-"open-source") open source philosophy which makes forked projects like Palemoon possible (I personally prefer Palemoon at the moment due to more conservative release cycle and UI plus strong security focus)
On the other hand, I wish Palemoon didn't exist: It's a compatibility nightmare for anyone trying to build HTML5 apps or games using recent APIs. All his changes tend to cause mysterious memory usage/cpu usage issues or simply break things, and 'use a different browser' is not a great answer to have to give a customer.
I don't know how you could consider Palemoon security focused unless everyone using it is building it from source and they've carefully examined his changelists. At least with trunk Firefox you know the commits are exhaustively reviewed and tested (perhaps too exhaustively; some FF contributors find the extensive review process stifling).
EDIT: Removed complaint about Pale Moon builds not being reproducible; he used to have a big angry rant about how he wouldn't share his build settings with anyone, but he's apparently removed it. Nice move!