This can be caused by a problem with the color profile for your display monitor or color profiles embedded in images.
You can disable color management to test that.
You can set the pref gfx.color_management.mode to 0 on the about:config page to disable Color Management.
You need to close and restart Firefox to make the change effective.

See:

• http://kb.mozillazine.org/gfx.color_management.mode

To open the about:config page, type about:config in the location (address) bar and press the "Enter" key, just like you type the url of a website to open a website.
If you see a warning then you can confirm that you want to access that page.

• Use the Filter bar at to top of the about:config page to locate a preference more easily.
• Preferences that have been modified show as bold(user set).
• Preferences can be reset to the default or changed via the right-click context menu.

Hi cor-el,

I just done that and the problem is still happening. Have you got any other ideas?

Thanks

Try to disable hardware acceleration.

• Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available"

If disabling hardware acceleration works then check if there is an update available for your graphics display driver.

Thank you when I turn it off it solves the problem, I also had an update for my graphics card. It still does it when I turn it back on though? Is this an important feature?

It never used to do this when I had Windows XP installed on this machine.

Thanks