One thing I disliked about the search suggestions was the occasional suggestion that felt like an advertisement, even though I knew the extension wasn’t trying to display ads. Specifically, suggestions for the Kohl’s and Macy’s shopping sites (whose URLs I was never trying to type, and which I never want to visit on this particular Firefox profile).
For example, when I typed “k”, intending to search for some history item, I saw a recommendation for http://www.kohls.com/. I guess that’s understandable; it’s a popular site. But annoyingly, not only did the recommendation have a large image of the Kohl’s logo, but I remember its title being something like “Shop at Kohls.com – Expect great things”. The inclusion of Kohls’ advertising slogan made the suggested result feel too much like an advertisement.
I don’t like advertisements because they put me in an adversarial mood, in which I fight the author’s suggestion to buy something because I know they don’t have my best interests in mind.
If you ever do more experiments with suggestions, I would suggest seeing if results could be displayed more factually, with fewer of the website’s own words. I would have been bothered less by seeing something like “Kohls.com [shopping category]”. Though showing a smaller logo could also help, making the logo small would probably hurt the situation where the logo helps the user confirm that the suggested site was the one they were thinking of.