Not true anymore ...
Whilst what the author said in that thread may have been applicable to earlier versions (>7 or 8), it's most definitely not been the case since v.9. Check and compare the 'Configure arguments' details in about:buildconfig to see what's been disabled (excluded) in Waterfox and Pale Moon compared to Firefox.
Run Peacekeeper and Dromaeo too, post your own results, if you like.