Pale Moon for Mac OS • How is PaleMoon 5 times smaller than Firefox on macOS?

I use PaleMoon as my regular browser and also have Tor Browser (Firefox) as my stand-by browser. While upgrading PaleMoon to 34.3.0.1, I observed that the latest version of Palemoon is only around 103+ MB where as the latest version of Tor Browser (Firefox) is around 503+ MB - that's 5 times bigger than PaleMoon! Even though I had deleted the Tor module (around 70+ MB) from the Tor Browser, I thought maybe the large size is just particular to the Tor Browser. So I downloaded the latest version of Firefox (macOS), and to my surprise, that is also around 503+ MB.

Now, I know that while PaleMoon is a fork of Firefox its codebase has diverged from it. But even without the code for something like WebRTC, WebExtensions and DRM media extensions, is there any particular technical decisions that have made PaleMoon / Goanna 5 times smaller than Firefox / Gecko?

(Kudos to the PaleMoon team for that)!