Why do you think Pale Moon depends on Firefox?
Basilisk, Pale Moon, and WaterFox all depend on Firefox because their development teams are far too small to keep up the development of a fully-fledged browser. They're going to have to rebase on the latest Firefox code eventually. No doing so will mean the browsers stagnate and fall even further behind.
Additionally, the XUL based add-ons will need developers to maintain them. No one is going to be interested in doing that in the long term because the user base is too small. NoScript is a good example of this. Giorgio Maone has committed to maintaining the old XUL based version of NoScript until June, 2018 after which he'll just focus on the current WebExtensions version.
Your fears are totally warranted
Meh. Doesn't look much different to the current UI. His fears are overblown.
Every point release in the past two years has reduced functionality.
What functionality has been reduced?
Basilisk, Pale Moon and Waterfox is preserving XUL in the browser
Only in the short term. They're all dependent on Firefox's upstream development so in the long term they'll become like Firefox is now or they'll stagnate and die.
On Firefox, I installed NoMiner - Block Coin Miners.
Why? You could just use uBlock Origin with the NoCoin block list. What does NoMiner do for you that uBlock Origin doesn't?
Even if it could perhaps be disabled, it will likely be impossible to remove all traces of its code from one's system.
But it still has to be able to detect that the code is even there.
It's just a block list. Specifically, this block list. You can make use of the NoCoin block list in, for example, uBlock Origin.
Opera isn't doing anything particularly special here and it's a shame that they don't give the block list author any credit in the blog post (though they do in the comment section and in opera://about/credits in Opera 50 beta itself).
make NoScript and other real tracking protection not work anymore all in the name of "speed."
Firefox has tracking protection built-in. Set it to "always" and it will be on in both normal and private browsing modes. NoScript works in Firefox 57+ and the author of NoScript says Firefox has "the best Browser Extensions API available on any current browser".
Your claims don't match up to the practical realities. Just use Firefox and be happy.
I judge a religion as being good or bad based on whether its adherents become better people as a result of practicing it. - Joe Mullally, computer salesman