LibreWolf

Its something to do with about:config but am unsure what setting it is

Using Fennec I asked deepai.com:

why does deepai not work with librewolf?

It answered:

DeepAi may not work with Librewolf due to several possible reasons:

1. Compatibility: DeepAi may not be fully compatible with the specific version of Librewolf you are using. Librewolf is a privacy-focused fork of Firefox, and some changes made in Librewolf may affect the functioning of web services or APIs, such as DeepAi.

2. User Agent: DeepAi might check the user agent (a string identifying the web browser) to ensure it is compatible with their service. If Librewolf uses a different user agent compared to mainstream browsers, DeepAi may not recognize it and may refuse to work.

3. Enhanced Privacy Settings: Librewolf takes privacy more seriously than mainstream browsers and includes additional privacy-focused settings by default. Some of these settings can restrict certain website functionalities or block specific web APIs that DeepAi relies on.

In case DeepAi is not functioning properly in Librewolf, you can try the following:

1. Use Mainstream Browsers: Temporarily switch to a mainstream web browser like Mozilla Firefox, Google Chrome, or Microsoft Edge to ensure DeepAi works properly.

2. User Agent Switcher: Install a user agent switcher extension in Librewolf and set the user agent to a recognized mainstream browser user agent. This may trick DeepAi into thinking you are using a compatible browser.

3. Contact DeepAi Support: Reach out to DeepAi support and inquire about compatibility with Librewolf. They may not officially support it, but they may provide guidance or suggestions to make it work.

Remember, compatibility with specific browsers or forks depends on how individual services are designed, and it is not uncommon for certain services to be optimized only for mainstream browsers.

So it works on some Firefox derivates, at least.