I was trying to add a favicon to my acp, and followed the instructions, debug on, then Developement > Admin templates > PAGE_CONTAINER > added <href> line before </head>
Just under the texarea where template is edited there was "Add-on :" with a dropdown next to it, with "Xenforo" preselected .. I think this was my mistake, I selected the empty line above Xenforo as I wanted the favicon applied to all of my ACP.
Saved .. and then boom, loading of the ACP page stops at the horizontal menu
How can I fix this ?