BBEdit instructions

Only supported versions are v. 11 and 14.6+

Installing

Make sure you install the font.

Enabling

Run in your terminal:

defaults write com.barebones.bbedit "EnableFontLigatures_Fira Code" -bool YES

Source: https://www.barebones.com/support/bbedit/ExpertPreferences.html

This same preference works for TextWrangler.