Firebug already tries to be smart and does complete d
to display
. In case you type v
it completes to visibility
. The code for this can be found here:
So if you want to change these defaults, you need to change them within Firebug's source code and build it by your own.
The built-in DevTools currently (Firefox 33.1.1) don't have such logic and simply display the first option in alphabetical order. To get that logic improved you should file an enhancement request for them.