This is the power user search add-on you've been looking for. The add-on is already extremely powerful and feature rich and has many time saving features, and it's still growing. I absolutely love it! The developer is very friendly and likes to work on suggestions from users. I can only recommend. The current developer forked SPC after its precursor add-on, SSS (swift selection search) was abandoned (the developer stopped working on it). A lot of powerful features have been added, such as POST search. Adding a new search engine is quick - just right-click on the search engine's input box and select "SPC - Add search engine". There are performance improvements: for users with very many tabs, SSS used to freeze for several seconds when you edited anything in the options. The developer of SPC fixed that in short order after I reported it.

If you use this add-on, please make sure to donate a little via the "Contribute now" button on the Mozilla add-on page!