Same here. In addition, if I think I will visit certain website only once, I open it in private mode and disable umatrix for all domains in the site for a quick view.
I use Firefox containers along with cookie autodelete so each tab gets a clean slate unless I've auto-mapped it to a container (where I've white-listed cookies - eg. a Facebook container where I only visit facebook.com)
Much safer to disable umatrix in the normal tabs then.
I think you can obtain the same result with just uMatrix. Block cookies by default, and whitelist them in individual scopes so that they don't follow you anywhere else. Do containers provide any further benefit over this?
Much safer to disable umatrix in the normal tabs then.