Oy! Didjaknow, if you press the backspace key in Firefox it will take you back to the previous page you'd accessed from your current tab? Just like clicking on the left arrow at the top of the window.
Except that this is currently broken in Linux versions of Firefox, and, by extension, Swiftfox. Fortunately, there's an easy fix, as is pointed out in the article: under about:config, change the value of browser.backspace_action to zero. Thank you, ubuntonista.
P.S.: From the comments, I learn that Alt-Left Arrow also goes back. Logically, Alt-Right Arrow goes forward. Since I'm an old Emacs-do-everything-from-the-keyboard person, I'm mortified that I didn't figure this out myself.