From Bugzilla Helper: User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:0.9.3) Gecko/20010801 BuildID: 2001080110 Since Mozilla v0.9.3 Backspace key does not return to previous page. With Mozilla v0.9.2 Backspace key still "worked". Reproducible: Always Steps to Reproduce: 1. Click a web URL 2. Click a link. 3. Press backspace key on the keyboard. Actual Results: Nothing happens. Expected Results: Jump to previous HTML page (like the menu GO / BACK does).
Taken from bug 92920: This is not a bug, it's a feature. This keymapping was causing user confusion, so it was taken out. See bug 69981 *** This bug has been marked as a duplicate of 92920 ***
Also note that you can go back by pressing ALT+[left arrow key] and forward by ALT+[right arrow key]. And read the comments towards the end on bug 92920. There is some discussion about setting your own keymapping with a link.