Doesn't work for me, firefox keep using the standard zoom based on percentage (not smooth).
Please let me know if there are updates.
PS. The "browser.gesture.pinch" are all settled as default

Thank you for the support!
I'm sorry to write here, please let me know if there are better ways to comunicate.

I'm using Windows 10, with the last Firefox version available.
here is the status of the browser.pinch.*:

_in; modified; string; empty;
_in.shift; modified; string; empty;
_latched; default; boolean; false
_pinch.out; modified; string; empty;
_out.shift; modified; string; empty;
_threshold; int; 0