Distribution engines are currently not being marked as built-in.

We regressed this here in bug 1405670 (the changes in the two sections after the highlights):

https://searchfox.org/mozilla-central/diff/47b9babf07b15b7bb6f7e873c87cd2ceddd1d4ec/toolkit/components/search/nsSearchService.js#3383,3408

The main effect of this, is that if the user removes a built-in engine that has been added or modified by a distribution, then we'll re-add it after update.

STR

1. With a Firefox distribution that is 59 or later, set up a profile, and remove one of the search engines that the distribution alters/adds.
2. Upgrade to the same Firefox distribution that is based on 69 or earlier (69 has another bug that makes things worse).

Actual Results

The engine that was removed re-appears.

Expected Results

The engine that was removed stays hidden.

https://hg.mozilla.org/mozilla-central/rev/85b2d74f7451

== Change summary for alert #25518 (as of Mon, 30 Mar 2020 22:17:31 GMT) ==

Improvements:

19% raptor-tp6-binast-instagram-firefox fcp macosx1014-64-shippable opt 290.77 -> 234.17
16% raptor-tp6-binast-instagram-firefox macosx1014-64-shippable opt 386.18 -> 326.04
14% raptor-tp6-outlook-firefox-cold fcp macosx1014-64-shippable opt 324.83 -> 280.42
12% raptor-tp6-outlook-firefox-cold macosx1014-64-shippable opt 438.42 -> 384.68
11% raptor-tp6-google-firefox-cold loadtime macosx1014-64-shippable opt 1,745.25 -> 1,553.42
9% raptor-tp6-google-firefox-cold macosx1014-64-shippable opt 626.52 -> 568.72

For up to date results, see: https://treeherder.mozilla.org/perf.html#/alerts?id=25518

Hi Florin, as much as I'd be happy to take credit for the perf improvements, I'm not convinced their mine. Unless those tests are doing something with distribution builds and search engines (which it doesn't look like), then this patch isn't related.

Looking at the related graphs, there seems to be in a lot of cases frequent dips in what the builders are reporting, and then they pop back up again. So I'm not sure, but this could be a false-positive.

Yep you are right re-triggered some tests and it looks like Bug 1578694 - Weekend performance spikes on mac
Sorry for the confustion