I use Waterfox, partly because it's a more modern fork (just prior to the removal of Tab Groups), and partly because it's easy to sync your old tabs and bookmarks from your old Firefox or Firefox-derivative browser.
I downloaded Pale Moon, but despite having its own Sync service, it only seems to be useful for syncing between other Pale Moon-using devices. It's also so old that it forked before Tab Groups was even a thing.