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Of course, the information on how to set the configuration is somewhere else. It took a little digging to find the Session Restore page at MozillaWiki, where they provide the configuration settings. The problem is that they don't tell you how to do this. If you restart from non-e10s mode, then closed windows are not restored.
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When you switch the '' pref to false and restart Firefox in non-e10s mode, the bad (e10s) session store is restored with closed windows. You can even set Firefox 2 to always restore your previous session instead of loading a home page, so you’ll never lose your place again. E10S Firefox restores all the previously open windows from the last session even when they were closed. Frustratingly, however, the blurb on the Firefox 2 Features page says that it should do what I want:
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Why software needs to be protected against crashing, rather than simply NOT CRASHING is beyond me. What Firefox's Session Restore feature protects against is accidental loss due to crashes (or other similar failures). However, you can make Firefox 2 always restore the previous session, even when you closed Firefox on purpose. Unfortunately, Session Restore was really written to handle crashes. I love this capability of SessionSaver in earlier versions of Firefox. People who have upgraded to Firefox 2 have raved about the Session Restore feature that restores all open tabs and even data entered into forms when Firefox is restarted. The first drop box asks what should happen "When Firefox starts." Set it to "Show my windows and tabs from last time." This is the same as the instructions below. UPDATE: This is set via the Main options screen in Firefox 2.
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