Aha. So, the problem only happens when there's an `about:config` tab (and possibly some other `about:something` tab), presumably because that's what it takes to trigger the `PrivacyFilter.jsm` code. And the tabs that disappear are all the ones after (and including) the `about:config` tab. So what seems to be happening is that under normal circumstances, an exception happening during session store prevents the entire store from happening, but on shutdown, the store still happens, with the state built until the exception happened.
Bug 1553417 Comment 22 Edit History
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Aha. So, the problem only happens when there's an `about:config` tab (and possibly some other `about:something` tab. EDIT: this may require the page to contain a form), presumably because that's what it takes to trigger the `PrivacyFilter.jsm` code. And the tabs that disappear are all the ones after (and including) the `about:config` tab. So what seems to be happening is that under normal circumstances, an exception happening during session store prevents the entire store from happening, but on shutdown, the store still happens, with the state built until the exception happened.