I think I would love to use this, but since my computer has memory problems, this causes Trello to be even heavier than it already is -- because it has more cards now.

Hmm, that's surprising to me, since all the cards are loaded into the DOM regardless of whether or not the extension is active. The only memory footprint should be from the extension itself, which should be minimal since the code is so simple.

In fact, you might even observe a speedup because fewer elements are being painted, but the difference as a whole should be marginal.

Are you experiencing actual slowness from using the extension? I'd be really curious to know.

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?

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.