No outline boxes in browsers - very odd

Now this is odd.

On my Mac, in Firefox, Chrome or Firefox, I cannot see the background lines and shadings on some web pages.

This happens on the Google homepage but I really noticed for all the admin buttons / functions / background shading in the Wordpress dashboard.

I've emptied the cache, verifed all my disk permissions, done a force refresh on Firefox.

On a friend's Mac all the pages, even the Wordpress ones that I login to, appear fine.

Any clues anyone?

I'm confused by what you mean 'background lines' Are you on a MacBook Pro to where you can hook up an external monitor to see if there is something wrong with your display? Does this only happen on the web, or is this a video issue throughout the entire computer?

Could you take a screenshot (Shift - Command - 4) of both your issue and a working site?

Screengrabs of windows with no background graphics

Here are some screen grabs from my iMac in my office with the graphics missing in my browser and the same webpage from my iMac at home.

Remember, I get the same issue with Firefox, Safari and Chrome.

****ed if I can work it out...

Another grab...

This is the odd looking one...

Even stranger...

The Google home page screen grab seems OK (see above) here but the Wordpress screen grab is only 6k - you can't really see what I mean.

Basically, all the grey shading and outlines for the boxes where you enter text etc, is all missing.

Apart from the text on the Wordpress page, the webpage for my Wordpress menu page (and all other pages) appear mainly white.

They both look the same to me, Is there anything that you might have changed on your resolution (contrast, brightness, etc) that would have affected this?