STR:

• Open Firefox View
• Intermittently/under certain circumstances you may see a "Sit tight while your tabs sync" loading message + an animated loading spinner in the "Tab pickup" section (I'm not sure yet how to reliably reproduce this state)
• Click the ^ button to the right of the section header to hide the loading message
• Click that button again to re-show the loading message

Expected results:

The loading icon should still be animated/spinning

Actual results:

The loading animation is no longer working and the icon is static, which has the slightly disorienting effect of making it look like an un-clickable refresh indicator

I expect this is quite a rare edge case because it relies on 1. the tab pickup data taking a long time to load and; 2. the user feeling compelled to toggle that section. When it does happen though, it kind of makes it feel like the loading has stalled and the icon looks a lot like a refresh button.

It looks like this is actually a known issue with animations in <details> elements that is specific to Firefox. There might not be any work to do except for wait on a more general fix, but I guess this could provide an excuse to poke that CSS Transitions and Animations bug which has been inactive for a couple years.

I think this should be fixed in 106 now that Emilio changed the <summary>/<details> implementation. Hanna, can you verify this?

I can confirm this is fixed by the <summary>/<details> implementation changes (and that it's no longer possible to reproduce the underlying issue of tab pickup data taking a long time to load - I had to make a code change to trigger the loading state to get the animation to show/persist).

Excellent, thanks Hanna!