Q:

Firefox can't display math in wikipedia.org

When I try to open a wikipedia page with equations I see just blank space in their place:

Although I can see png and image files in other wiki pages.
I checked permissions in Tool > Page Info and everything is set to Default. In about:config, permissions.default.image is set to 1.
I've also tried to run Firefox in safe mode with no luck.
I'm using Ubuntu 16.04 with Firefox version 46.0.1

A:

I had the same problem today and I finally found the issue. The equations generated by mathML on Wikipedia use the default color for text with a transparent background. If the default text color is white, you can't see the text because Wikipedia background color is also white.
To fix this, you must change the default text color to black.
see: https://support.mozilla.org/en-US/kb/change-fonts-and-colors-websites-use#w_change-font-color
Try to unset "use system colors", because some dark themes use white text as default. Set the text color to black and the background color to white.

