You can try these steps in case of issues with web pages:

You can reload web page(s) and bypass the cache to refresh possibly outdated or corrupted files.

• Hold down the Shift key and left-click the Reload button
• Press "Ctrl + F5" or press "Ctrl + Shift + R" (Windows,Linux)
• Press "Command + Shift + R" (Mac)

Clear the cache and cookies only from websites that cause problems.

"Clear the Cache":

• Firefox/Tools > Options > Advanced > Network > Cached Web Content: "Clear Now"

"Remove Cookies" from sites causing problems:

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

You can start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance).

• Do NOT click the Reset button on the Safe Mode start window.

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

The problem is exacerbated by "This Connection is Untrusted" preventing me to even enter the 'Add-ons Manager'.

Any help appreciated. It appears I need to turn off the 'untrusted' barrier so that I can "switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance".

Check the date and time in the clock on your computer: (double) click the clock icon on the Windows Taskbar.

Check out why the site is untrusted and click "Technical Details to expand this section.
If the certificate is not trusted because no issuer chain was provided (sec_error_unknown_issuer) then see if you can install this intermediate certificate from another source.

You can retrieve the certificate and check details like who issued certificates and expiration dates of certificates.

• Click the link at the bottom of the error page: "I Understand the Risks"

Let Firefox retrieve the certificate: "Add Exception" -> "Get Certificate".

• Click the "View..." button and inspect the certificate and check who is the issuer of the certificate.

You can see more Details like intermediate certificates that are used in the Details pane.

If "I Understand the Risks" is missing then this page may be opened in an (i)frame and in that case try the right-click context menu and use "This Frame: Open Frame in New Tab".

Note that some firewalls monitor (secure) connections and that programs like Sendori or FiddlerRoot can intercept connections and send their own certificate instead of the website's certificate.

I've done all you have suggested and continue to get white background page with black text and some blue which are hyperlinks. This even applies to the support page that I am now typing in. It doesn't happen for the majority of my web pages within firefox but does for BT Email / Firefox Add-ons - "Get Add-ons" and as above the support page. Any further help would be appreciated.

Make sure that you haven't enabled a High Contrast theme in the Windows/Mac Accessibility settings.

• http://windows.microsoft.com/en-US/Windows7/Make-the-computer-easier-to-see-optimize-visual-display

Make sure that you allow pages to choose their own colors.

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

Note that these settings affect background images.

See also:

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

Hello,

I did everything you said and it did not work.

I found the solution through Google Chrome. Somehow my computer acquired a 'Proxy Server'. I turned it off and the problem disappeared.

This looks like a problem a few other users have suffered and the solution I found may assist.

I went to:

Tools / Options / Advanced / Network and ensured 'Use System Proxy Settings' was selected.

Hope this helps.

I also had this problem, or something looking very similar. It has apparently gone away after deleting Firefox, then removing the folders C:\Program Files\Mozilla, C:\Program Files (x86)\Mozilla and C:\Program Data\Mozilla, rebooting and reinstalling Firefox.

Not sure if this was a coincidence, but it was not cleared by just deleting and reinstalling FF.