Go to about:config and set extensions.webextensions.tabhide.enabled to true, then restart your browser.

I've added an option for setting a keyboard shortcut in v0.0.12. However, the necessary API is only implemented in Firefox 60, so you will need to update to the beta before you can use the new option.

You can only use shortcuts which are not used by the browser - Ctrl+Shift+E is already taken, and it seems that Ctrl+E also doesn't work for Windows users.