For years I was using Multi Smart Search. I recently upgraded from Firefox 49.0.2. to Firefox 55.0.3 and found that Multi Smart Search doesn't work with it at all. I found Context Search to be identical to what I had before, so I'm happy. :)
The only thing I would change is what the menu item says. Right now it just says, "Search for *searchstring*. I think it should say, "Search for *searchstring* using...". So, add the word "using" with the ellipsis. Or, even "on..." instead of "using...".
So for example: searching for the word" Firefox" would make it say, "Search for "Firefox" using...", or "Search for "Firefox" on...".
I guess there's one other thing I would change, if it's even possible: make this include right-clicking links. The default search in Firefox will search the text of links when simply right-clicking the link.
Anyway, yeah, this is a great extension.