With fire gestures in Firefox you can highlight a block of text and then gesture right (or whatever you have assigned) and all of your mycroft search engines you have installed from here:
http://mycroft.mozdev.org/dlstats.html
will come up in a pop-up and you can click on one to search a specific engine for the highlighted block of text. Possible with Smooth Gestures?

Looking for similar functionality. In firefox I use drag de go, which lets you configure a search engine to go with gesture right, left, etc. So for example you can set it up to highlight text, gesture left, and search imdb.

No gestures, but Context Menu Search works well.