Addon somehow makes page elements appear at the wrong depth.

[FrobtheBuilder]

I know this sounds ridiculous, but when I have Tab Center Redux visible in the sidebar, the ordering of text and images on web pages gets messed up, and text that's obviously supposed to be behind higher elements appears on top!
I tested this extensively and found it to only happen when Tab Center Redux specifically is being rendered in the sidebar. With it hidden, or the sidebar set to anything else, it doesn't occur.
I believe this behavior is limited to Nightly so far, but I'm sure the change that caused this to start happening will make its way downstream eventually and more people will see this odd behavior.

The image below shows what the Firefox homepage looks like when this bug is present, the bar at the top is supposed to be overlaid on top of the text below it, but they're rendering on top instead. This seems to affect other pages with overlays such as this similarly.

And for comparison, the content when the sidebar is set to something else:

This may in fact affect all addons that use the sidebar, I haven't tried it with any others. I will investigate further. I still feel it's worth bringing to the attention of this project, even if it is indeed a regression in Firefox itself.

[FrobtheBuilder]

It happens with Tree Style Tab too. This must be a Firefox problem. We need to report this to Mozilla.

[FrobtheBuilder]

https://bugzilla.mozilla.org/show_bug.cgi?id=1553007