Footnote.com is not always the easiest site to search in my opinion. I usually browse using the main page until I get to the era I want for the database I'm searching. Then when I'm on that specific database, I search just that database. Personally I rarely search the entire database because I am not happy with the ways to refine searches.
If you've had difficulty using Footnote.com you might want to try searching specific databases instead of the whole site. Even that has problems, but I've generally had better luck tackling specific databases.