Mobile: It is not possible to scale forum pages and pop-ups

Steps to reproduce:

1. Go to home page of Jcommune forum
2. Do tests from the table below.
   For Android 4.2.2:

   Test	Chrome 34.0.1847.114	Default browser 4.2.2-WW-epad-10.10.10.3.39-20131220	Firefox 28.0.1
   Try to scale homepage in vertical position	FAIL	PASS	PASS
   Try to scale "Log in" pop-up in vertical position	FAIL	PASS	PASS
   Try to scale page in horizontal position	FAIL	FAIL	PASS
   Try to scale "Log in" pop-up in horizontal position	FAIL	FAIL	PASS

   For iOS 7.1.2:

   Test	Safari	Chrome 35.0.1916.41
   Try to scale homepage in vertical position	FAIL	FAIL
   Try to scale "Log in" pop-up in vertical position	FAIL	FAIL
   Try to scale page in horizontal position	FAIL	FAIL
   Try to scale "Log in" pop-up in horizontal position	FAIL	FAIL

Actual result: Pages and pop-ups don't scale in some browsers and devices.
Expected result: Pages and pop-ups should scale in every browsers on all devices

The same behavior in all forum's page and with all dialogboxes