The following ones are supported:
Bing, Ecosia, qwant, google and startpage.
In addition it allows you to add custom bangs to these sites (via the preferences page of the add-on).
It also allows you to change the bang prefix (e.g. # instead of !)
Source: https://github.com/sophie-glk/bang

Install

• License: MIT License
• Weekly downloads: 7
• Average daily users: 140
• Rating: 4.9091/5 of 11 ratings
• Created: 2019-01-21 21:48:14
• Last updated: 2023-06-25 12:10:42
• Homepage:
• Support site and email
• Orig: https://addons.mozilla.org/en-US/firefox/addon/tt7753bang/
• API: bangs@tt7753