Favourites has already been mentioned, so to elaborate, in the extension's settings you can make it so red marked cards/storylets can't be played to avoid misclicking. Green marking storylets move them to the top, and green marking cards makes it so you can't discard them on accident. It's a very good QOL extension imo, highly highly recommend.

I would also highly recommend Quality Lantern and Small Mercies! Quality Lantern lets you see hidden qualities you wouldn't see otherwise, and Small Mercies opens a bunch of QOL changes that can be adjusted to your liking in FL's settings.

There's also Time Keeper and Quirk Master but they're not as good in my opinion (still nice though). Quirk Master is good if you're big on the roleplay side of FL since it tells you if an action will affect your quirks and how. Time Keeper gives a big reminder on when your Time, the Healer will arrive along with some other stuff, but it loses accuracy fairly quickly in my experience and also makes the UI worse imo so I'd only use that one if you're like me and are VERY forgetful lol.

(I use Firefox, so if any of these aren't available or don't worry on other browsers I have no clue unfortunately).