This is very similar to bug 1735495. What happens is tab processes failed to load one of the essential XPCOM modules such as nss3.dll or xul.dll while the browser process loaded all of them. That black popup is "Couldn't load XPCOM" opened [here](https://searchfox.org/mozilla-central/rev/b697834e78a3ef7613e2fa57c07624b1d9d1c909/browser/app/nsBrowserApp.cpp#242). In bug 1735495, the reporter said the issue was gone for some reason and unfortunately we couldn't finish investigation. Marc, thank you very much for your cooperation. Can you follow the steps of https://bugzilla.mozilla.org/show_bug.cgi?id=1735495#c26 to capture DLL loader's debug trace?
Bug 1753910 Comment 8 Edit History
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This is very similar to bug 1735495. What happens is tab processes failed to load one of the essential XPCOM modules such as nss3.dll or xul.dll while the browser process loaded all of them. That blank popup is "Couldn't load XPCOM" opened [here](https://searchfox.org/mozilla-central/rev/b697834e78a3ef7613e2fa57c07624b1d9d1c909/browser/app/nsBrowserApp.cpp#242). In bug 1735495, the reporter said the issue was gone for some reason and unfortunately we couldn't finish investigation. Marc, thank you very much for your cooperation. Can you follow the steps of https://bugzilla.mozilla.org/show_bug.cgi?id=1735495#c26 to capture DLL loader's debug trace?