Is there a keyboard shortcut to close the current Debugger (source file) tab within the Firefox Developer Tools (on MacOS)?
On Windows it is Ctrl+W, so I assume it is Cmd+W on MacOS.
Note that you need to have the file you want to close focused in the DevTools, otherwise the browser tab will be closed.
See also the documentation of all DevTools keyboard shortcuts on MDN or the one just for the Debugger.