Devtools.inspector.enable no longer allows you to remove inspect element from contextmenu.
marking as a duplicate of bug 736465. Please add comments there as-needed. Thanks!
This is actually a valid bug. It won't be resolved by bug 736465. But it is not a Firefox bug but a Firebug bug.
Patch committed to Firebug source tree: https://github.com/firebug/firebug/commit/b96acf4ab6eb53308eada491e6a7ae1a2e186dba Will be part of Firebug 1.10.1 Honza