Weird Javascript problem on Safari and other web browsers

Question

Hello,
this is actually pretty weird. For the past several weeks I have been dealing with a very strange problem which I believe relates to JavaScript. To be more specific I have an issue with two websites: Macuser.gr and Facebook.com.
As far as Macuser.gr is concerned this is how it's supposed to look:
http://f.cl.ly/items/0j1J123Y2D0t1C2U3b1f/Screen%20Shot%202013-02-06%20at%202.25 .04%20PM.jpg
and this is how Safari renders it:
http://f.cl.ly/items/3N0V3I1c0Q0a1r0K0e1C/Screen%20Shot%202013-02-06%20at%202.25 .40%20PM.jpg
The problem is with the preview images as you can see.
Now, in Facebook there's this annoying white line where it isn't supposed to be:
http://f.cl.ly/items/0k0i2c0T0q1h3t2j2s3e/Screen%20Shot%202013-02-06%20at%202.25 .52%20PM.jpg
I have tried and tested everything (Guest user, different browsers etc) and all it comes down to is JavaScript. Disabling Javascript seems to fix everything immediately. Enabling it again and this mess occurs. Also, this happens with the latest versions of Safari, Chrome and Firefox BUT not with Camino 2.1.2 although it has JavaScript enabled in it.
This is really frustrating and it appeared out of the blue one day. I did not have this problem from day 1. Any ideas?

Answer 1

Boot into Recovery by holding down the key combination command-R at the startup chime. Release the keys when you see a gray screen with a spinning dial.
Note: You need an always-on Ethernet or Wi-Fi connection to the Internet to use Recovery. It won’t work with USB or PPPoE modems, or with proxy servers, or with networks that require a certificate for authentication.
From the OS X Utilities screen, select Get Help Online. A clean copy of Safari will launch. No plugins, such as Flash, will be available. While in Recovery, you'll have no access to your saved bookmarks or passwords, so make a note of those before you begin, if they're needed for the test.
Test. After testing, reboot as usual and post the results.