I often do searches with multiple search engines and extras with the same query but with site:reddit.com added at the end. Being able to press CMD L to focus the URL bar, and then CMD C with all the text selected would make things a lot faster. This was added months ago to Firefox but it looks like it was removed now.
Not sure about what was removed but you can use the keyword bookmark with your own search url replacing the search term with %s
For example add bookmark:
So in the address bar you would type the keyword first then the search query like: