It actually doesn't show too bad. So I would anyway rewrite this message.
- First, why absolutely say Chrome ? Especially if it actually works in Firefox.
- Second, well, even if I wanted, I can't download Chrome on Windows Phone, so I would say that you should detect when it's a smartphone and show a different message then.
- Third, I can understand that it's a lot of work to support all of those platforms, so I don't necessarily expect that you fix the issues with Windows Phone, but that really irritates me when people always advise to download Chrome. This is not IE 6 times anymore, we should all learn from it :)
It shows the banner in IE but then it is actually very slow.
I believe the tone of the message is to take the onus to the developer - if they had more time, or if your browser respected standards moar, you would be able to visit the website without caring about which browser you use.
Front-end development, with the variety of form factors and browsers can be a thankless task which not many people respect - I think their message could be far worse personally.
Sorry I am too lazy to care about browser specific web sites.