It does not depend on the browser whether you can drop the www or not.
E.g. www, shorty, loki, ragtime are sub-domains of the domain mudcat.org.
Most servers for a domain are configured to use subdomain www as a default so it does not matter whether you type www before it or not.
It is possible (but rarely used) to have more than one level of subdomains - some people have urls like www.firstname.lastname.de, so the domain name is lastname, firstlevel subdomain is firstname, secondlevel subdomain is www.

Most ISPs only support subdomain www for private homepages as this makes their server admin easier.

MudGuard