Rated 5 out of 5 stars

As far as I can tell, the only extension that gives you multiple context search engines without a sub-menu. Plus it works on editable text too.
The only extension I have that was worth forcing compatibility force Firefox 4 rather than finding an alternative. Would love an official update though.

This review is for a previous version of the add-on (4.0.1). 

Hidden potential Rated 5 out of 5 stars

I basically use thing as a multifaceted replacement for the normal “search google…” right click context menu. I found that the easiest way to add any search under the sun, without mucking about deciphering urls yourself, is as follows:

Install “SearchWith*” (https://addons.mozilla.org/en-US/firefox/addon/2194), and in the config you will find an abundance of ready made search engines that you can copypaste into the 4 available within DictionarySearch. If you can’t find the search you need simply go to http://mycroft.mozdev.org/, install the search you want into firefox, then import it into searchwith and copypaste it into dictionarysearch.
Finally, uninstall or disable SeachWith and use “Menu Editor” (https://addons.mozilla.org/en-US/firefox/addon/710) to ditch the original context search.
This may seem a bit longwinded and backassward, but it works for me ;)

As for a review; this is the only addon I wish I could install twice. Seriously, the only thing that could make it better is having maybe 6 or 8 search options.

*Searchwith is a similar, and worthy, solution to right-click-searching but uses a nested menu to choose the search, which is why I prefer DictionarySearch. However, if you want lots (4+) search options it may be ideal for you.

This review is for a previous version of the add-on (3.0.0).