Make sure that you allow pages to choose their colors and that you haven't enabled High Contrast in the Accessibility settings.

• Tools > Options > Content : Fonts & Colors > Colors : [X] "Allow pages to choose their own colors, instead of my selections above"

• http://kb.mozillazine.org/Website_colors_are_wrong
• http://kb.mozillazine.org/Websites_look_wrong

Thank you for the suggestion, but I already have these settings. The problem is that some web pages now appear very undetailed. There is no graphic design, background colours, fancy texts etc. It is just a problem with some sites. Do you have any othe suggestions? Thank you for your help

Clear the cache and the cookies from sites that cause problems.

"Clear the Cache":

• Tools > Options > Advanced > Network > Offline Storage (Cache): "Clear Now"

"Remove Cookies" from sites causing problems:

• Tools > Options > Privacy > Cookies: "Show Cookies"

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of the extensions or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes).

• Don't make any changes on the Safe mode start window.
• https://support.mozilla.com/kb/Safe+Mode

Can you attach a screenshot and post a link?

• http://en.wikipedia.org/wiki/Screenshot

Use a compressed image type like PNG or JPG to save the screenshot and make sure that you do not exceed the maximum file size (1 MB).

You did check the Windows Accessibility settings in the Control Panel?

Thank you very much! clearing the cache fixed the problem.

You're welcome