Rated 4 out of 5 stars
Would be perfect except for one thing: It doesn't respect my preference to switch to the new tab I just opened. So, I middle click the search engine, but I can't immediately see the results. I then have to click the tab that just opened. I would prefer that tab to be opened automatically (according to my Firefox preference). (Note to Ben Basson, the contact link on your page appears to be broken.)This review is for a previous version of the add-on (0.4.4).
Dan, left clicking the search engine should respect your tab preferences. Middle clicking inverts that preference.