One of the greatest mysteries to me is why most file managers don’t have tabs - it makes performing tasks so much simpler.
I’ve found a lightweight file manager for Ubuntu called PCMan that gives you most of the functionality from Nautilus, but also has tabs.

"You owe a lot to your tabs in Firefox. Without them you would have a desktop filled with clutter. So why not do something nice for your tabs and give them a few tweaks? ..."

Firefox only (Windows/Mac/Linux): Firefox extension Find In Tabs searches for text across all of your open Firefox tabs. It does so by adding a Find in Tabs button to the find bar that switches from the normal single-page search to a multi-tab search.

Do you spend most of your day with five or more Firefox tabs open as you research on the Internet? Then you're probably a candidate for Tabs Open Relative.

Firefox includes an option for bookmarking all open tabs, but heavy users of tabs will find that this option is hardly enough. When you are researching a subject, the particular combination of tabs matters as much as the individual ones -- and, besides, selecting the tabs to open individually can be tedious if you are dealing with several dozen.

All the cooler kids may be Firefox devotees, but I'll happily admit to being a fan of Internet Explorer 7 on Windows Vista. I like almost everything about it, from its layout to its tools to the way it handles tabs. There is, however, one thing about Firefox I really love and wish was in IE7.

After a recent update of Firefox I found that the Tabs Open Relevant add-on (see review here) had ceased to work. Having grown used to this extension to the point of dependency, I was once again swamped with a vast number of confusingly sorted tabs.

Firefox only (Windows/Mac/Linux): Experimental Firefox extension TooManyTabs organizes extra browser tabs in Firefox, allowing you to store over 50 extra tabs in a special row for quick access at a later time.

If you are a Firefox power user like I am, then you probably have dozens of tabs open all the time. After trying a number of different options, I've finally settled on using multiple rows of tabs as the best option.