Interesting topic about possible death of Pale Moon because of that specification and their inability to adopt it:

https://www.reddit.com/r/palemoon/comments/fk4fnl/attention_...

Who knows the Palemoon team realizes pretty fast that when the developer is writing something like that here - https://forum.palemoon.org/viewtopic.php?f=1&t=24004

that it has the meaning that they can't move forward or have serious issues in attempting to do so. Google-Web-components... The next BIG thing in web development which is used in Youtube and other big pages will be most likely Palemoons undoing. Without it - no more videos on Youtube! Media and business sites are no longer loaded and can't be used properly, buttons can't be pressed anymore so pages are partly or fully broken! This is what more and more pages adopt, as it is the NEXT BIG THING! The Palemoon team failed in the past to implement highly complex features and the only solution so far was in the end to adopt fresh engines from Mozilla on a regular base, something which is NO LONGER POSSIBLE as future Firefox engines have not the features the Palemoon team sees as vital! Get slowly ready to start the search for a new browser to which you can switch in the near future - the best and most logical time in doing so is NOW!

Additionally - regarding this whole topic: https://freenode.logbot.info/binaryoutcast/20200314

WHY it most likely will die... While we all should be grateful for Gaming4JC and his attempts to bring over some code lately - Google Web components is TOO BIG - Seamonkey guys don't have it inside their new new 2.53 - which is based on Firefox 56. Waterfox - using the same code - also has issues. And if it is already problematic with Firefox 56 based code... how big is the chance to succeed with Firefox 52 based code? With the help of only one skilled guy? My suggestion is try as much as other possible browsers now to make the switch when it is forced on you as less annoying as possible.