I tried your changes. Your userChrome.css breaks containers though, as it hides the container color from the tabs. Your changes also breaks all the privacy controls you can get from Firefox on a per site basis. I think if someone tried your css and chose very strict privacy options they're not going to have any way to see that privacy control options may have broken a page. Those things in the address bar are vital.
I highly recommend people to not use this css unless they feel comfortable editing it to unbreak things and don't want any of the per site options. This UI change reduces the usability of Firefox to the point I would consider it broken.
If you don't like the container colors in the tabs, you can edit them to be colors you prefer.
You’re right that it removes the color bars, so I’ve commented out that line as optional. But as far as I know, this CSS doesn't hide any site-specific privacy-related controls. Which ones are you referring to?
Note on the color bars: I'd rather not have extra noise in the tabs because I determine which container I’m in through the address bar and automated domain containers. Of course, for someone who wants an overview of how many tabs are in each container, the color bars might be useful. It's a good point that this might be unexpected, even though it's noted in the CSS. So I've commented out that line and will let people enable it themselves.
I'm sorry I was mistaken on the per-site privacy controls being removed. I can't edit the comment to fix my mistake. The controls didn't appear on a page that I thought it would, but I found another and with your css it was still there. My mistake.
I highly recommend people to not use this css unless they feel comfortable editing it to unbreak things and don't want any of the per site options. This UI change reduces the usability of Firefox to the point I would consider it broken.
If you don't like the container colors in the tabs, you can edit them to be colors you prefer.