Unfortunately, this add on makes Firefox unusable while it's enabled.

Great tool but just to slow to use :-(

Slows down the *entire* browser in Firefox 58 and up, somehow; long-standing and workflow-breaking UI bugs remain unfixed for months: https://github.com/zalmoxisus/redux-devtools-extension/issues/377

Good effort, but the author needs to pull their finger out and test in Firefox in addition to Chrome.