On Thu, 10 Nov 2011, Brian Wood wrote:

> I'm not up on all of the plugins so maybe this already exists. Often I 
> have an idea and go find a tab that I can use to research the idea. 
> After doing that for a few minutes or more I can't remember what I was 
> doing before or which tab I was in.  This is kind of like the back 
> button but for tabs.  Tia

Good question.  I guess this is what you want (assuming you are using 
Firefox):

http://gorgias.de/mfe/  <- look for "FLST"
https://addons.mozilla.org/en-US/firefox/addon/flst/
https://addons.mozilla.org/en-US/firefox/addon/focus-last-tab/

I don't know which is best, but they all claim to do what you want. 
Here's more info on the keyboard shortcut tricks built into Firefox:

http://support.mozilla.com/en-US/kb/Keyboard%20shortcuts#w_windows-tabs

Mike