Websites displaying wrong

Hi!

I bought a new router from netgear 4 months ago and since then I have had trouble viewing multiple websites:
Wordpress.com
9to5mac.com
Etc

First of all, here's a picture of how these websites look like (Many websites look perfect, or at least Normal)

9to5mac.com:

8211173153_be3e78650a_medium

9to5Mac (via Flornez)

My first step was contacting my internet provider, They told me the problem is the router "We do not support this issue"
This is true, I know the problem is the router, since I have changed the router with an older one and it works.
I then contacted Netgear (Which makes the router) and we probably had a 10-20 email conversation.
They wanted me to send them multiple Network traffic files (via Wireshark) etc
They gave me 2 other software versions that they wanted me to try without any luck. They then decided to make new software just for me, which took them 1 month. I received this software yesterday and after I uploaded the new software, still no change. I have contacted them again for further details but I am also making this forum post, in hope that someone out there has been in this situation and know how to fix it since it seems the netgear people doesn't really care.

(This problem occurs on Win7, Win8 and OS X, + multiple mobile devices and on Wired and wireless connection)

My router model: Netgear WNDR4000

Thanks.