Looks like Bug 1603778 is the culprit here. A try run that disables the Top Sites behaviour shows [mixed stylo results](https://treeherder.mozilla.org/perf.html#/compare?originalProject=mozilla-central&newProject=try&newRevision=d2a6b85f0e4c8493bb998971285169bb9fb8dd10&framework=1&selectedTimeRange=172800#table-header-2128255543), whereas a try run that disabled openViewOnFocus [shows clear improvement](https://treeherder.mozilla.org/perf.html#/compare?originalProject=mozilla-central&newProject=try&newRevision=6756fb56418020586df29ea00a5f369cc7abe316&framework=1&selectedTimeRange=172800#table-header-2128255543).
Bug 1606081 Comment 1 Edit History
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Looks like Bug 1603778 is the culprit here. A try run that disables the Top Sites behaviour shows [mixed stylo results](https://treeherder.mozilla.org/perf.html#/compare?originalProject=mozilla-central&newProject=try&newRevision=d2a6b85f0e4c8493bb998971285169bb9fb8dd10&framework=1&selectedTimeRange=172800#table-header-2128255543), whereas a try run that disables openViewOnFocus [shows clear improvement](https://treeherder.mozilla.org/perf.html#/compare?originalProject=mozilla-central&newProject=try&newRevision=6756fb56418020586df29ea00a5f369cc7abe316&framework=1&selectedTimeRange=172800#table-header-2128255543).