User Agent: Mozilla/5.0 (X11; Linux i686; rv:34.0) Gecko/20100101 Firefox/34.0 Build ID: 2014112600 Steps to reproduce: I found an article n tab groups, so I tried Ctrl+Shift+E. As I didn't know what to do there (the window displaying instructions was gone), I tried to "cancel" the dialog by pressing some close-like icon. Actual results: All my tabs were gone (really). Trying "History->restore previous session" was unavailable, and "History->Recently closed Tabs->Restore All" did not have the desired effect (still all tabs gone). Expected results: There should be minimum guidance in the tab groups dialog. When closing all tabs by mistake there should be an obvious way to restore them.