We’ve been working on a tool for measuring extensions/add-ons performance impact on a user - https://github.com/treosh/exthouse.
Image: Additional scripting work added by extensions to the main thread in Chrome.
It was possible to do for Chrome because it has extended API to measure performance, especially long tasks API.
It will be awesome to do the same for Firefox but currently, there is no API to do these kinds of measurements. Polyfills for interactive metrics also doesn’t work.
Referencing github issue:
Will be happy to hear community feedback about that idea and support to raise the question for API implementation priority