hello, firefox has an extended-support-release version that is intended for large organisations where an IT department is deploying browsers - this mentioned release is currently on version 31 and receiving security updates. for websites it is not possible to discern between the regular firefox 31 (outdated) and firefox 31 esr (current), that's why the site is telling you that the latest version is installed... in order to update, please see [[Update Firefox to the latest version]]