mw.loader: Guard against odd setTimeout behaviour in old Firefox

Bug: 46575
Change-Id: I80af730daa815f0c273fe942c570d1f0144bbbb1
Revert "mw.loader: Add debugging"

This reverts 8c566e5 and 91f4661.

Change-Id: If24993e57cc432c1ee2723e8354c034e7f5a2a76