Situation in SafeBrowsing: - We have cached completions. - We started up the browser freshly and haven't done any database updates. - We try to open a malware/phishing page. In this case, we'll return immediately from LookupCache::Has, without having probed the PrefixSet. This will cause the AddNoise lookup to fail as it will not know where to look for noise. Because we didn't do any database updates yet, the table will not be considered "fresh" and we need to do a remote lookup @Google despite having the completion. This remote lookup will be done without noise. This can probably be solved by just moving the check for completions as an additional check below the prefixset probe in LookupCache::Has, instead of having it replace it.

https://tbpl.mozilla.org/?tree=Try&rev=caa492f7913b https://hg.mozilla.org/mozilla-central/rev/a82389691227