On Windows and macOS (if using Plucky 1.0.16+), to enable Firefox support, invoke:
pluck + okfirefox and
pluck repair, and then restart Firefox after the delay has elapsed.
On most Linux distributions, Plucky should work with Firefox out of the box.
Whether Plucky will support Firefox in the long haul is yet to be determined. Mozilla’s current policies make doing so time consuming, and most people use browsers other than Firefox.
The author himself used Firefox for many years, but finally switched to Brave because it took so very long to address issues in Firefox.