I rather would use Pale Moon before i would touch Mozilla Firefox - Mozilla which killed almost all customization options just to be able to be as attractive to Chrome users as possible.
In fact, i also would use Vivaldi every day over Firefox. Mozilla has turned into a greedy sell-out developer with zero respect for power- or geek users!
The problem with this narrative is that it is entirely fictional. The web extensions addons that have replaced the old style are just as featureful and Mozilla has done a good job of providing the functionality to build powerful addons.
Example Pentadactyl -> Tridactyl, noscript, ublock origin, stylus.
I'm not clear where you are coming from with the "greedy" accusation nor where you get off calling them sell outs. Based on what?
Your refrains betray "reduced to 180 characters" level of understanding of the matter and I strongly suggest you gain a more complete understanding of technical and business matters before attacking people who are producing so much value for the open source community.
In fact, i also would use Vivaldi every day over Firefox. Mozilla has turned into a greedy sell-out developer with zero respect for power- or geek users!