I tried all of the things suggested here, including whitelisting evernote in Firefox security settings, to no avail. However, I did get it to work in Firefox another way, briefly. Once, when I used Bing instead of Google for a search I got the Evernote related content to show up. I could not reproduce that a second time though, even though searching the same thing. Very odd.
This leads me to thinking that the issue might be related to search engines. Perhaps Google wants to keep the real estate on our search page dedicated to adds and shopping? I'll keep experimenting with Bing search and see if I can get it to work again. Hopefully someone will help us recover this feature. I really miss it and would switch search engines for it.