[fiatjaf]

Yes, huge slowness.

I don't think all the cards are loaded anyway. I think Trello loads them as they are needed. Since the extension reduces the size of cards, it is as if the list was scrolled down, then more cards are loaded. Is that a possibility?

[imalex]

How many cards do you have in your list? I have a list of 75 cards and I'm not observing the lazy loading you describe.