This is the best pop-up dictionary app I've found yet! I love being able to customize what search engine I want a pop-up definition from. I just wish I didn't have to make two clicks to get a definition from the website I want though. It should have the option to be fully automatic with one click.

EDIT: I wonder if it's possible to add a button for this addon to the toolbar for the SSS addon?

https://addons.mozilla.org/en-US/firefox/addon/swift-selection-search/?utm_content=addons-manager-reviews-link&utm_medium=firefox-browser&utm_source=firefox-browser