App Store Connect drag previews/screenshots not working

Hi!

In App Store Connect - here - https://appstoreconnect.apple.com/apps/1563922454/appstore/ios/version/inflight - I am supposed to drag previews and screenshots in, in the form of image files I presume. But that is not possible. At least not here in Firefox 87.0 (64-bit), when dragging from Finder.
And when I press "Save" even the following text disappears:

" Drag up to 3 app previews and 10 screenshots here.
We’ll use these for all iPhone display sizes and localizations you select. "

So how am I supposed to enter the image files?

EDIT: After updating and restarting Firefox, now ver. 88.0, it suddenly works!
App Store Connect drag previews/screenshots not working
 
 
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