User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US) AppleWebKit/534.7 (KHTML, like Gecko) Chrome/7.0.517.41 Safari/534.7 Build Identifier: Build identifier: Mozilla/5.0 (Windows NT 5.1; rv:2.0b8pre) Gecko/20101103 Firefox/4.0b8pre about:blank Switch to tab option Reproducible: Always Steps to Reproduce: 1.Launch firefox 2.Open a tab and close the previous tab 3.in the new tab type in about:blank 4.an option "about:blank Switch to tab" is displayed 5.select this option Actual Results: Firefox window closes

I can confirm that this also happens on Mac OS X. It will close the tab on all platforms, but what happens after that is up to the current config of the user. If s/he has it set to close the window when the last tab is closed it will close the window and possibly Firefox if it is the only window open (Firefox does not exit on OS X however because Firefox can remain running without any windows open).

I think this disappeared with the fix for bug 598619