I recall using a very early version of tabbed browsing that arranged the tabs on the left by default instead of on top. I think this was Mozilla Browser on Red

I recall using a very early version of tabbed browsing that arranged the tabs on the left by default instead of on top. I think this was Mozilla Browser on Red Hat Linux 6, around 2000. At the time, neither I nor my computer was able to handle more than one website at once, so I didn't use the feature much!