[ndriscoll]

Firefox does support jxl (in the sense that the code is there and works), but it's disabled by default.

[account42]

So does Chrome if you check out the right commits and enable it.

But if you go getfirefox.com, click "Download Firefox" then there will be no JXL support not even behind any configuration flags. So no, it doesn't support it. There are also no plans to enable support with the current implementation.