Whatever you’ve done to UI must be some atrocity as I do not experience issues with FF. You’ve never specified which FF extension you’ve used that had slowed down your browser.

Chrome (and by extension) Chromium and all derivative browsers are Google’s lever to truly control and shape internet to their liking. Multiple people said it already.

Personally I find Chromium UI very cumbersome and dislike it a lot. Which is to say we all have our own preferences for UI.

In your case you’d have to weigh your repulsion with available performant FF UIs vs future of internet and choose which decision can you really live with.