Up until now, I have never heard of this setting, nevertheless it had gotten toggled a while ago. It had made me a little nervous during the last couple of weeks.
How I solved the issue:
- searched the web for “Firefox ignores stylesheets“,
- too many hits of course …,
- found a hint pointing to PrefBar,
- installed the Firefox Add-on by the name of PrefBar,
- toggled the Colors check box on that tool bar,
- which surprisingly did, what I had not expected.
But that did not reveil me, which Firefox setting was involved.
- So I launched about:config,
- filtered by “color“,
- toggled the Colors check box another couple of times on PrefBar,
- until I finally got aware of browser.display.use_document_colors changing its value simultaneously.
I have no idea, how this setting had gotten toggled a couple of weeks ago. Now everything is fine again.
What a wicked little thing!!
I am really relieved, this got finally solved.