Instead of opening new "issues" for general talk we can use this area for discussions, feedback and questions. Open new "issues" for real bugs and problems.

Trying to makes CSS code Firefox 57+ ready?
Remove all @namespace references. They are the reason, if your code refuses to work.

Application/hamburger button in tabs toolbar?
Look here: #46

Things this project will not target/recreate

• curved tabs
• old complete themes
• ...

Things not possible with CSS

• more toolbars like add-on/status bar (CSS can not create new toolbars)
  • displaying full sized status popup below window content is possible
  • moving bookmarks toolbar to windows bottom is possible
• new buttons (CSS can not create new buttons)
• additional menuitems (CSS can not create new items)
• old search (some things are not compatible to Fx 57+)
• custom/new/different functions for buttons/menuitems/menus
• activity indicator
• preferences window
• additional location bar
• favicon in location bar
• moving menubar items to a different toolbar
• restart button
• ... many more