The removal of the #fast-tab-tooltip flag has just destroyed my usual browsing habit. I frequently browse dozens of reddit boards/threads, for example, or open countless image tabs.
This feature is torpedoing my productivity by constantly drawing long lists over my screen, over and over. It's neither needed nor helpful - especially when it shows the tooltip even on a single tab. Yes, thank you, I can infer what I've got open from seeing the favicon and tab title, I don't need another box for it.
It's unnecessary, and having a setting to disable if so required was the perfect solution (although I wish it had been moved from flags to proper settings). Removing it does nothing to improve satisfaction with the browser. My solution for now will be to look into downgrading to another version / channel to restore my productivity short-term.