IPv6 vs IPv4

I am wondering if any of you that have your own router behind the TMHI gateway, have issues with regards to IPv6 vs IPv4. Here is what I mean...

Since TMHI doesn't support IPv6 PD, I have my own router pulling a IPv6 address from the THMI gateway, and then essentially NAT all the IPv6 traffic internally, so having my own IPv6 DHCP server, etc. This generally works well. Very well actually.

The issue I am running in to though, is not all web browsers tend to pick IPv6 as its primary.

For example with ipv6-test.com, in Safari on my MacBook Pro, it shows IPv6 is the preferred protocol with a fallback to IPv4. In Chrome and just about any other browser, the primary is IPv6, and no fallback to IPv6, although it shows IPv6 is supported.

At the end of the day, I am wondering if I have some incorrect setup on my IPv6 DHCP setup, and if anyone has any ideas. More curious than anything. My current setup doesn't have any major performance issues.