It's possible that the dialog is displaying the actual setting incorrectly. If you switch one or both checkboxes (page colors, system colors), OK that, then return to the dialog and switch it again, does that have any effect?

A standard diagnostic step is to try Firefox's Safe Mode to see whether it is caused by a custom setting or add-on.

First, I recommend backing up your Firefox settings in case something goes wrong. See Backing up your information. (You can copy your entire Firefox profile folder somewhere outside of the Mozilla folder.)

Next, restart Firefox in Safe Mode using

Help > Restart with Add-ons Disabled

In the Safe Mode dialog, do not check any boxes, just click "Continue in Safe Mode."

If links are colored correctly, this points to an add-on or custom setting in your main Firefox 11 profile as the problem.

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

See also:

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

Thank you for your replies. Running in safe mode does cure the problem. However, if I run in normal mode and disable all the extensions and plugins, the problem still persists. I have checked the about:config entries and I can't see anything that might affect the link colors. Interestingly, changing the link colors in the dialogue box (or in about:config) has no effect on the website colors. Links are still blue/purple. Perhaps this is a clue?

Try to disable hardware acceleration.

• Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available"
• https://hacks.mozilla.org/2010/09/hardware-acceleration/

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

• https://support.mozilla.org/kb/how-do-i-upgrade-my-graphics-drivers

Thank you for your help, but in the end I uninstalled Firefox (after saving my bookmarks) and did a clean install. It's fine now.