Sea Containers

What it does

Opens a sidebar to manage containers

To open the sidebar use Ctrl/Cmd+Shift+Period.

Requires Firefox 54 or later
- Download Beta
- Download Nightly Firefox
Requires containers enabled
Go to about:debugging
Load Temporary Addon
Click the manifest file in this directory
As this is a debugging extension, it wont last after a restart.
- This is currently going through review process to be installable through addons.mozilla.org

Firefox lets users override 'chrome' level styles. Add a chrome directory and create a chrome/userChrome.css file with the following contents:

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul");
#TabsToolbar {
  visibility: collapse;
}

When firefox is reloaded you won't have any horizontal tabs.