The idea is like Firefox Safe Mode, so you can temporarily disable all gadgets and user scripts (and probably styles too) to see if a bug is reproducible without them.
There is no other way to do this, except:
- Individually unchecking all the gadgets (while noting which you had checked) (you can also reset all preferences, but that's not acceptable except for very new users).
- Manually modifying all the user script pages (common.js, vector.js, global.js, etc.)
- Making sure you hard refresh/clear your cache
then undoing all that.