User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9) Gecko/2008052906 Firefox/3.0 Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-GB; rv:1.9) Gecko/2008052906 Firefox/3.0 when closing firefox it remembers the tabs that you had open in that session for the next time you restart firefox. if you have a popup window open as well as your main(initiating) window, and you close the main window first, followed by the popup, firefox will only remember the information from the popup on restart and you will lose the tabs that you had open in you main window. Reproducible: Always Steps to Reproduce: 1.set firefox to remember your tabs on next restart. 2.browse to a page that causes popup windows. 3.initiate a popuop window. 4.close the primary window. 5.close the popup. 6.restart firefox and only the information from the popup window is remembered. Expected Results: ideally firefox will be able to link a popup to another instance of firefox and identify it as a subsidiary and remember the information and tabs from the initiating window. this bug is rated as critical simply because it is possible to lose the data open in you primary window.