Localhost redirects to https but Chromium does not

My guess would be that at least one of the sites you developed and connected to on localhost had the HSTS header header set. The result of Firefox reading that header would be

The HTTP Strict Transport Security header informs the browser that it should never load a site using HTTP and should automatically convert all attempts to access the site using HTTP to HTTPS requests instead.

To fix this on Firefox, open the browser history by pressing ctrl+shift+h. Next, locate any localhost site you've visited and right-click on that site. Lastly, click on Forget About This Site

To fix this on Chrome, go to the location bar (ctrl+l) and type chrome://net-internals/#hsts. Next, go to the Delete domain security policies-header and type localhost and click delete. If you want to see what headers are set for localhost first before you remove them, use the query-functionality under the Query HSTS/PKP domain-header.

The last thing you should do is figure out which of your sites sent/are sending the HSTS header in the first place. I don't know what language your backend is running, but something like Spring Security will add the HSTS header by default when enabling web security, for instance using the @EnableWebSecurity annotation.