Something's definitely misbehaving in Firefox on the page. Using a mouse to highlight text in a comment and then trying to move the highlight to the next paragraph, the selection jumps to the first paragraph as soon as the cursor leaves the `span` of each paragraph.

From a quick look at the DOM, I'd bet dollars to donuts it's the weird combination of custom WebComponents and the #shadow-root stuff and other various markup excess that they just didn't bother to test with Firefox. Whether it's a bug with Firefox itself and how these elements are handled, I guess would need some investigation. But if it were my web app, I'd probably just fix it instead of blaming the browser.

Screen capture: https://imgur.com/RmoSZRB

Works fine in Firefox, too.