Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:88.0) Gecko/20100101 Firefox/88.0 ID:20210310215846

Today I have seen that for a single tab only the history navigation doesn't work. While the back button is enabled, and also the history entries aer correctly shown when opening the drop down, any click on the button doesn't cause any navigation back in history. Also selecting a specific entry is a no-op. When opening new tabs the navigation works fine.

In this specific case I (probably) did the following steps:

1. Searched for a specific bug mail from Bugzilla in Gmail (pinned tab)
2. Clicked the link to the bug in that email so that a new tab got opened
3. Scrolled down the Bugzilla page to the comment mentioning the landing commit on mozilla-central
4. Clicked the hg.mozilla.org link.

And after that navigating back doesn't work.

I can still click on other links or enter URLs in the locationbar to cause navigations that correctly populate the history. But for each loaded page the back button doesn't cause a back navigation.

The only way to get back/forward navigation working was to close the tab, and to reopen this recently closed tab.

Right now I'm not able to reproduce it again.

This is a SHIP bug.

Olli says Henrik tested history.back() in the console and it did not work.

I have a theory here that requestedIndex isn't updated or rather not cleared in some case.

whimboo saw this again and requestedIndex was in fact wrong. It was 0 when it should have been -1.

I think there might be a case for the issue happening also without SHIP, but
since it is way less asynchronous, triggering that issue is hard.
So the patch and test are for SHIP only.

https://hg.mozilla.org/mozilla-central/rev/1968ba484b6f

Backed out changeset 1968ba484b6f (bug 1697905) on dev's request

Backout:
https://hg.mozilla.org/integration/autoland/rev/5c28878ca6adc5155c1d30d75983794b1822310b

Backout merged to central: https://hg.mozilla.org/mozilla-central/rev/5c28878ca6ad

https://hg.mozilla.org/mozilla-central/rev/cd1fcf6de563