Excellent Rated 5 out of 5 stars
I'm not too keen on having the selected text displayed in the context menu name, but in this instance it does make sense because the word "on" has been added to the end. It's also truncated reasonably, so it doesn't make your context menu width go too crazy.
I would have to say that SmartSearch is probably my favourite extension of its kind. It's very easy to use and has useful options (particularly the one to have no context menu when no text is selected). The engines are easy to configure (standard Firefox quick searches) and you can also group your entries by folder. It also doesn't rely on the engines listed in your search bar (so you can organize them differently to suit your specific needs).
I highly recommended this extension.