browser.safebrowsing.remoteLookups works indeed, I could confirm this using Fiddler. For some reason, Notepad++ couldn't find a mention of 'remoteLookups' in sources.
> time egrep -Rni remotelookup .
./toolkit/devtools/gcli/source/lib/gcli/types/selection.js:81: spec.remoteLookup = (typeof this.lookup === 'function');
./toolkit/devtools/gcli/source/lib/gcli/types/selection.js:128: if (this.remoteLookup) {
egrep -Rni remotelookup . 2.01s user 0.32s system 99% cpu 2.346 total
