Before bug 1506608 landed, we were flipping the remoteness of the initial tab, which caused us to hit this part of the codebase: [1]. shouldActivateDocShell would return true, and bam, the docShellIsActive property would be set to true. Because we don't flip remoteness for the initial tab (which is a good thing), we never hit this code path, so the property is never touched. What's particularly troubling is that the TabParent and the underlying DocShell are out of sync - TabParent's mDocShellIsActive member defaults to false[2], but DocShell's mIsActive member defaults to true[3]. That's what Gijs was seeing in comment 1. Given how close we are to the uplift, here's what I suggest: 1. We paper over the issue the safe way by setting the docShellIsActive property on the TabParent for the initial tab manually. 2. File a follow-up bug to reconcile the initial active states between TabParent and nsDocShell. [1]: https://searchfox.org/mozilla-central/rev/bee8cf15c901b9f4b0c074c9977da4bbebc506e3/browser/base/content/tabbrowser.js#1697-1701 [2]: https://searchfox.org/mozilla-central/rev/bee8cf15c901b9f4b0c074c9977da4bbebc506e3/dom/ipc/TabParent.cpp#158 [3]: https://searchfox.org/mozilla-central/rev/bee8cf15c901b9f4b0c074c9977da4bbebc506e3/docshell/base/nsDocShell.cpp#366
Bug 1520791 Comment 3 Edit History
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Before bug 1506608 landed, we were flipping the remoteness of the initial tab, which caused us to hit this part of the codebase: ([1]). shouldActivateDocShell would return true, and bam, the docShellIsActive property would be set to true. Because we don't flip remoteness for the initial tab (which is a good thing), we never hit this code path, so the property is never touched. What's particularly troubling is that the TabParent and the underlying DocShell are out of sync - TabParent's mDocShellIsActive member defaults to false ([2]), but DocShell's mIsActive member defaults to true ([3]). That's what Gijs was seeing in comment 1. Given how close we are to the uplift, here's what I suggest: 1. We paper over the issue the safe way by setting the docShellIsActive property on the TabParent for the initial tab manually. 2. File a follow-up bug to reconcile the initial active states between TabParent and nsDocShell. [1]: https://searchfox.org/mozilla-central/rev/bee8cf15c901b9f4b0c074c9977da4bbebc506e3/browser/base/content/tabbrowser.js#1697-1701 [2]: https://searchfox.org/mozilla-central/rev/bee8cf15c901b9f4b0c074c9977da4bbebc506e3/dom/ipc/TabParent.cpp#158 [3]: https://searchfox.org/mozilla-central/rev/bee8cf15c901b9f4b0c074c9977da4bbebc506e3/docshell/base/nsDocShell.cpp#366