Oh, I assumed UrlbarProviderTabToSearch adds two results for some searches since it has two different chunks where it adds results, but that's not true. It's incidentally adding two results because `UrlbarSearchUtils.enginesForDomainPrefix()` can include the same engine more than once in the array it returns, which seems like a bug.
Bug 1744367 Comment 16 Edit History
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~~Oh, I assumed UrlbarProviderTabToSearch adds two results for some searches since it has two different chunks where it adds results, but that's not true.~~ It's incidentally adding two results because `UrlbarSearchUtils.enginesForDomainPrefix()` can include the same engine more than once in the array it returns, which seems like a bug. Edit: It can add multiple results per search of course, by design (see bug 1647927). What I'm seeing is that Google ends up being added twice due to what I mentioned above. So there are two concerns here: (1) Fixing that duplication bug, (2) modifying the muxer for TTS as mentioned in comment 14.