User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-GB; rv:1.9.1) Gecko/20090624 Firefox/3.5 Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 6.0; en-GB; rv:1.9.1) Gecko/20090624 Firefox/3.5 In preferences, I have "Always show the tab bar" activated. Back in FireFox 3.0 (the last version I used), when only one tab is open, I could still close it and I would see a blank page. This may look like nothing, but I actually use this short-cut a lot to stop pages from loading or simply put FF on "standby" instead of closing it. In FF 3.5, we can no longer close the last tab using this method. CTRL+W still works, I believe. Reproducible: Always Steps to Reproduce: 1.Leave one single tab open 2.Try closing it with Middle Button 3.Also try to close it via "Close This Tab" Actual Results: You can't. Expected Results: The tab should close.
Changing the preference browser.tabs.closeWindowWithLastTab in about:config sets this back together.