Palemoon was interesting at a time regular Firefox was very slow (Gecko engine so before Firefox 57).
Since Firefox Quantum engine implementation THIS IS NO MORE A PROBLEM, please try to forget Palemoon
Most of old extensions (scripsafe, noscript, ublock....) have been ported to the new extension model
For light browser alternative on FreeBSD the best is
www/falkon, formerly known as "Qupzilla" which is now deprecated
Falkon is a Webengine (the official reworked Chromium Blink engine for QT, and so perfectly stable) based browser, more stable and lighter than Chromium.
Falkon and Mozilla Firefox are according to me the two current references for FreeBSD
There is also Otter-Browser, which is more experimental. The main interest is that you can switch between Webengine (based on Blink, forked from WebKit) and Webkit (the regular Apple's Webkit)
Waterfox IS TOTALLY USELESS on FreeBSD.
Waterfox uses the very last Mozilla Gecko engine.... and so was also affected by its incredible slowness.
On the contrary Palemoon team long time ago locked on a quite older version of Gecko not affected with theses speed issues.
They renamed this engine "Goanna"
Mozilla foundation doesn't support anymore any Gecko engine.... so these forked engines may have PLENTY of security holes.
Waterfox is just packaged by one simple guy... do you seriously think that "one" man could now efficiently maintain such a big thing as Gecko engine ????????
Waterfox was long time ago nothing other than the very first 64 bit implementation of Firefox on Windows at a time Mozilla was still focusing on 32 Bit only for Windows, but did support a regular 64 bit *nix version. So basically.... Waterfox has nothing to do with *nix
Palemoon is a bigger project so with (a little) more people in the team, but team can't compare with the Mozilla foundation. We can still wonder if they are really enough to efficiently maintain the old Gecko fork facing security issues.