I think he meant a few checkboxes, for choosing things like round corners etc. which should not be too hard. Really necessary?
Maybe not, but you should realize, that you have a shrinking core group of users, while liked Firefox because they could modify it the way they wanted - and therefore did not liked it, when frequently changes broke their setup.
Which is unfortunately an inherent problem with our legacy customization approach.
And it is clearly not something the vast majority of users want, if they left Firefox for another browser that appears to them less customizable but more stable. We have run numerous user studies about what users actually care for and they have all informed what Firefox is going to be in the future.
So does not particularly well thought out criticism.
There's also shrinking core group of users, who liked Firefox before it fell back on many areas, crippled by having to maintain compatibility with add-ons that relied on internal workings. We realize that very well.
Configurability comes with an exponential testing and maintenance burden. So no, it's not just adding a few checkboxes. It's what happens with those afterwards.