The idea that while browsing online you may decide to search for a word or lookup a place on a map. This add-on let's you highlight a word, sentence or whatever and a tooltip pops up with options. By default you can 'Copy', 'Search' or lookup in 'Maps' the highlighted text. The available options in the tooltip can be changed or new ones added from the settings popup.
The Popup Tooltip allows domain exceptions where you don't want this to run. Just in case it interferes with some websites.
Example:
This extension is now published here (for Firefox): https://addons.mozilla.org/firefox/addon/popup-tooltip/
and here (for Chrome): https://chrome.google.com/webstore/detail/popup-tooltip/opbiebgbaablkfhomifdkhjdbilobbdg
Privacy Policy: https://github.com/kjabr/Popup-Tooltip-Firefox-Extension/wiki/Privacy-Policy