Hi Cocosilk, what happens when you try clicking Enable for any of the themes. Nothing at all? An error message?

Do all three of the built-in themes (Default, Light, Dark) work?

Have you noticed any issues with Extensions?

(I think the horizontal lines are there to show the text color that will be used in that area.)

The default theme doesn't work at all and when I attempt to install any theme, the base color of the theme will show but nothing else of said theme (design, animation,etc.) does.

The extensions work fine.

The strike-throughs never showed up before on the themes before installing them, so something happened after the latest update that screwed up the themes.

Hmm, I don't know what would cause the themes to load incompletely.

Do you ever create a userChrome.css file to modify your toolbar area?

In case there is a conflict or incompatibility between Firefox 67 and your graphics card/chipset software, you could try disabling Firefox from using hardware acceleration. This article has the details: Firefox's performance settings.

I'm attaching two screenshots illustrating what I mean about the white and black lines showing the text colors.

Changing the performance settings fixed the problem.

Thank you for all your help! :-)

Hi Cocosilk, thank you for the report back. Hardware accelerate improve font smoothing and video performance -- when it's working -- so if those begin to bug you, you might check this article: Upgrade your graphics drivers to use hardware acceleration and WebGL.