I added a search engine. I had the right %s URL string. When I added it, Firefox Focus said "make sure you replace the search string with %s". That made me think it was checking the URL, so I added https:// in front, BUT I accidentally removed the first letter of the URL. It let me add it, but then searches didn't work. It letting me use the typo implies it doesn't check the URL. A novice user may not realize that the error really means "add https://" not the catch-all "check your %s". Not sure where to report bugs, so I'm adding it here. The workflow to fix my typo could also be improved upon. It's dark-pattern adjacent to have to go in to search settings, change the default to another engine (assuming there is one), get kicked back to main settings, then have to go back to search engines, remove the one you added, then add it again. Could be fixed by having Focus actually try the URL when adding one. I think adding offline would be a very infrequent use case, but you could make it prompt "Hey, I can't load this URL are you sure you want to add it?"