Problem accessing website from Firefox and Chrome

Question

Hi !

First, sorry to write in english. I am located in Canada and have a website in China.

I'm using a CDN to provide content to China (Cloudfront). I also have a database in Singapore.
Javascripts are loaded from Google, and I ping a webservice to know if the user is from China or another country.

Users are able to connect to my website with Sogou, in 3-5 seconds, but with Chrome and Firefox, it takes over 50 seconds.

Is there anything I should know about Firefox/Chrome in China ?

Thank you!