Was able to confirm SHIP causes the regression.
Bug 1944579 Comment 4 Edit History
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Was able to confirm SHIP causes the regression. `window.history.length = 1` with SHIP disabled and `window.history.length = 2` with SHIP enabled.
Was able to confirm SHIP causes the regression. `window.history.length = 1` with SHIP disabled and `window.history.length = 2` with SHIP enabled. It appears SHIP enabled starts out with `2` as soon as the page is loaded.
Was able to confirm SHIP causes the regression. This seems specific to Fenix: `window.history.length = 1` with SHIP disabled and `window.history.length = 2` with SHIP enabled. It appears SHIP enabled starts out with `2` initially. On GV, visiting the same page: `window.history.length = 1` on both cases. Can't truly reproduce on GV because a custom error page is involved, but it is suspicious that the initial counts on Fenix aren't as expected.