Recent Commits to firefox-csshacks:master

autohide sidebar: Move some of the custom variables under #browser

This allows us to use them targeting #sidebar-container as well

Add sidebar_buttons_above_sidebar.css

non floating tabs: Override the background for default non-system theme

non floating sharp tabs: set --split-view-padding-block: 0

We already behave as if the value would be 0, and actually setting
the variable to 0 makes things like tab-separator-lines scale correctly

tab separator lines: Show separator at front of split-container having multiselected tab

Fixes #680

tab separator lines: Add back the header that had accidentally been removed