User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8b2) Gecko/20050608 Firefox/1.0+ Build Identifier: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8b2) Gecko/20050608 Firefox/1.0+ If you open a link in a new window and subsequently a link to an image on that page the back button remains disabled. Reproducible: Always Steps to Reproduce: 1. Visit http://www.technorati.com/cosmos/search.html?rank=&url=thatonegirl.net 2. Right-click "Recent Posts (Tim Hatch)" and open in new window 3. Click a link to an image. Actual Results: Observe back button is still disabled after clicking the link to an image Expected Results: Since I've had two states in this new window, I should be able to go back one. I have browser.sessionhistory.max_viewers set to 1. Workaround is to use the Go menu, which is across all windows.
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.7.8) Gecko/20050511 Firefox/1.0.4 WFM
It turns out it is caused by the Tidy HTML validator extension.