It's a bad trade off. Every security related bug Firefox fixes is a how to guide for ruining waterfox users day for anywhere from weeks to years.
This will grow increasingly challenging if the code bases diverge in order to keep old school add-ons working given that waterfox has virtually no man power.
One solution would be to have a dedicated computer which is considered compromised from the start. Don't store importent stuff there, don't do money related activities etc. This way you have a convenient browser for 99% of the time - without stupid restrictions and Mozilla control.
This is a highly impractical way to live life just to make some stand. It's cutting one's nose to spite one's face.
There are other actively maintained browsers with plenty of eyes on them and manpower behind them, many with vibrant plugin ecosystems, just use one of those.
This will grow increasingly challenging if the code bases diverge in order to keep old school add-ons working given that waterfox has virtually no man power.