MacOS Theme with condensed native sidebar

[rtgibbons]

I've been using Sideberry for a while and tweaking the themes of it and Firefox to find a pleasing setup. I think I've finally found a good solution. Having the tabs act as a "tab" to the browser window while also providing subtle color for the container. Then still allowing access to the native sidebar for quick access to those features.

I was manually applying rounded corners on the browser content, but recently found out about sidebar.revamp.round-content-area. If you wanted a custom radius size, the CSS is still in UserChrome.css.

I don't think anything other than Vertical Tabs in Firefox is required. Don't think there are any custom changes in other Sideberry settings that are needed either.

Changes are at https://gist.github.com/rtgibbons/8cf727b60ec7770ac75b48f5be50d316