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.
I’m not sure I fully understand your requirement so this may not be what you’re looking for but CTRL+k brings you straight to search and puts the cursor in the URL bar. The engine is to the left and can be selected.