Vlad I took a look at it. It manages the two modes as I expected - you need to physically "close" the find in page to get back to the main address bar. It's not the best experience because it removes what makes the address bar easy to use, which is optimization for a single task (change what address I'm looking at). Here the user has to think about what mode that field is in. In general, the less optimized a UI element is for a single task, the more complex (and thus the more work) the user needs to do to use it.
Imagine a search bar in a web page also changing the website you're on. It's an extreme example, but it's apt: the in-page search field always searches the site you're in. It's optimized for searching that site. The browser address bar is optimized for going to an address. (This is part of the reason why other browsers put the "find in page" UI a little into the viewport – it helps tie the relationship between that field and what it searches.)
I don't know if you care about this, but this type of mode switching is also not that accessible.