I'd make this a poll, but polls can't include images.

Firefox. I have clicked "ALT" on a post image and the pop-up alt-text window contains more text than will fit. I have hovered the mouse over the empty lower section of the scroll bar (you can see that it is fully expanded; I have indicated the mouse cursor with a "+").

What will happen when I click the lower section of the scroll bar?

1. Window scrolls and stays open.

2. Window scrolls but instantly closes.

#mastodonbug

You guessed it. The answer is 2. The pop-up window scrolls, then instantly closes.

That's, uh, surprising. Please don't surprise the user on long-established UI.

(I can scroll the window by clicking, holding and dragging on the *top* half of the scroll bar. That's beside the point; it's a workaround.)