The Linux users aren't the only ones with optimized FF builds any more !
It's a Firefox build optimized for Windows, with a few useless features (Parental control things, and accessibility) removed.
It's a bit faster (~5% faster at SunSpider on my system), seems more responsive, and uses a little less memory.
However, if you are using an old processor (e.g. Pentium III), it won't work.
You can even install FF's language packs (PaleMoon is only in English by default) and replace the icons using ResHacker if you don't like the PaleMoon logo
And since it's a Firefox build, it will use your existing Firefox profile - that's useful.
I'm posting this using Pale Moon
PS : But don't expect a miracle - it still has the issues Firefox has with memory management