Uploading images using firefox

Is anybody else having issues uploading images to discourse from clipboard if using Firefox? Works fine if I swap to Chrome but FF gives me:

image

Works fine for uploading saved images, just not pasting them from clipboard. I swear it used to work recently.
FF 94.0
Linux Mint 20.2

No error for me here, native Firefox and Flameshot screenshots pasting from clipboard upload just fine. What's the format of the images you upload? The size?

FF 94.0
Kubuntu 21.04

Makes no difference, first time was a large image but to get that error I took a really tiny screen snip to upload and it still failed.
No issue in Chrome at all using the exact same method (which is how I got the image in there).
Also took a selection from GIMP to see if it was something to do (somehow) with the screenshot tool but did the same thing.

A dumb suggestion but who knows: does cleaning up cookies for discourse makes a difference?

Nope, still broken... weird. Even tried turning off an extension I added recently and no luck there either.