ctrl-L now clears the URL bar in 151.01

Apparently `keyword.enabled` had been set to `true` in a recent update, as a new default. I found this via [https://support.mozilla.org/en-US/questions/1301742 this other support question]. I searched for the config key and it showed in regular text, indicating it's the default and thus I didn't change it. Switching it to `false` and then `true` restores the old behavior.