Alternatively you could use Firefox's Container Tabs.

This works especially well when combined with the Cookie auto-delete extension.

Link: https://addons.mozilla.org/en-US/firefox/addon/multi-account...

You can use NoScript to control which domains you want content loaded from and what type.

It's often necessary to allow same-host scripts for extensions or bookmarklets to work. Those some-host scrips are often a considerable part of the problem.