Please do not alter debug settings unless you know what you are doing. If the viewer “breaks”, you own both parts.
Some settings may have side effects, and if you forget what you changed, the only way to revert to the default behavior might be to manually clear all settings.
Debug settings are accessed, in Firestorm, from the Advanced menu. If you cannot see this menu in the menu bar, press Ctrl-Alt-D. Alternately, you can bring up debug settings by pressing Ctrl-Alt-Shift-S.
The following is a list of default settings used by various viewer modes:
See this page for documentation on earlier versions of Firestorm.