For example, '.es' for ES6 JavaScript.

@christopherbalz -- could you please provide us a sample test case or URL where you are facing the issue , so that it helps us in triaging the issue better.

Thanks !

Create a file named something.es and put the following inside -
function d()
{
 alert('The script ran.');
}
for (let i = 0; i < 1; i++)
{
 d();
}

Open the Developer Tools, go to the Sources panel, right click on the left navigation pane and click on Add folder to workspace, select the folder that has the something.es file you created earlier. Find something.es in the pane, double click on it and see the it shows the code without syntax highlighting (all of the content has the same font color).

Note that if you load a page that loads something.es as a script (<script src=something.es></script>), syntax highlighting does work, so it is a workspace issue.

What are the other extensions you use for javascript?

I think mapping options should be provided in addition to good defaults (js, jsm, jsx perhaps, es).

Bulk closing low-priority issues with no activity. Please re-file and refer to the closed issue if it's essential to fix.