Provides a keyboard shortcut (Shift + Alt + C by default) to create a new tab that retains the current/last-used container.
You can edit the default shortcut under Add-ons and Themes > Extensions > ⚙️ > Manage Extension Shortcuts > Retainer. New tabs can be restricted to the last-used container in the extension's preferences panel under Add-ons and Themes > Extensions > Retainer > ⋯ > Preferences.