Looks like the issue is that the submitted link is a search for “you.com”, which appears to be a special search result that includes prominent promotion of the Chrome extension, regardless of which browser you’re using. It would probably have been a better idea to submit a link to the landing page or a normal search result.
Edit: it badgers me to install it in Chrome even in mobile Safari.
Edit 2: seems there is a search box on top of the page. It works but I didn't notice it initially because
- the page was so intensely focused on getting me to install a Chrome extension (both in Firefox on iOS and Safari on iOS)
- and the placeholder text ("you.com")looked like a decoration initially (try something like "type here" or something)