“Firefox lets you tinker with many of its internal settings by
entering about:config in the address bar. The preference settings
exposed on that page let you make many changes, but the tabular
interface is not exactly user-friendly. One alternative, the
Preferential extension improves matters only slightly. The
Configuration Mania extension helps sidestep some of the learning
curve, but it’s no panacea either.“After you install it, you can invoke it by selecting Tools
-> Configuration Mania. You will be presented with five tabs:
Browser, Security, HTTP Network, UI, and Debug, with Browser as the
displayed default…”