WideGPT by Chris Stone

IMPORTANT NOTICE FOR EXISTING USERS: OpenAI changed ChatGPT's url, which breaks the domain-specific permissions granted to WideGPT by Firefox. Because of this, you will need to give permission to WideGPT to access data on the new domain. In Firefox, go to add-ons and themes > WideGPT > Manage, click the gear icon, and select "Check for updates...". You will be prompted to grant permission for WideGPT to access data on the new url.

WideGPT adds a slider for adjusting the width of ChatGPT answer space. The slider can be found on the bottom of the sidebar of ChatGPT (ctrl+shift+s to open).

Source is available on GitHub.