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.org/kb/Safe+Mode

• 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.

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

You can use the NoSquint extension to set font size (text/page zoom) and text color on web pages.

• NoSquint: https://addons.mozilla.org/firefox/addon/nosquint/

Hardware acceleration didn't work, and also safe mode there was no change... Tried NoSquint also did not work..

Three preliminary remarks:

1. Windows sucks;

2. Firefox, as consequence, sucks too (but, honestly, I didn't think it sucked that hard: lack of basic programming skills and, above all, common sense);

3. You (or someone/something for you) probably changed "Window Color and Appearance" settings (as I did, which brought me to hell for a good half an hour in Firefox).

Solution:

1. Windows will continue to suck till the end of the ages, so put your mind at rest;

2. Having been released eight years ago and presenting still a basic, but major issue like this one denotes that also Firefox will continue to suck (in this respect) for a long time onward, so be indulgent and forgive all these sinners;

3. Right-click on Desktop -> Personalize -> Window Color -> Message Box -> Color -> [whichever colour except clear ones]. Restart Firefox.

Done. Your redeemed Internet browser is then revived and you are restored in life; through the aging, the fearing, the strife.