I'm all for change that improves usability, efficiency, and performance, for instance. I'm not for changes that obviously inhibit such things, like the changes that Mozilla has made recently.
about:config is not as convenient to use as a checkbox in the preferences dialog. If what you're suggesting were actually true, then there'd be no need for a preferences dialog at all, and all users would configure Firefox using about:config. But we both know that isn't true. It is not convenient to remember the name of a specific about:config option, especially when the names change periodically. Even filtering by part of the option name isn't convenient, as that requires remembering Mozilla's terminology, and using a general term like "javascript" still leaves many options to sift through manually.
As for the status bar, the URL popup shown when hovering over links is much less usable than the status bar. It is harder to quickly focus on, for instance. Having to remember yet another obscure keyboard shortcut for functionality that should be enable by default, like the addon bar, does not promote usability, as well.
The menu bar is not a "waste of space" because it more than pays back its cost by making a huge amount of commonly-used functionality very easily accessible. It is especially valuable because of the cross-application conventions it embodies, making it take even less effort to perform common tasks.
We shouldn't have to manually enable core functionality like menus or the status bar, for example. Such functionality should already be enabled by default when Firefox is first installed. Anyone who doesn't like the menu bar or the status bar should have the option to disable them, of course. But they should not have been disabled by default, or even removed completely.
