I thought I posted this earlier, but I think I created a support ticket by mistake?
Sometimes when uploading a post with an image -- and I feel like anecdotally it happens more often when there are also embeddable links? A post will just hang indefinitely in the upload process.
Sometimes when this happens, the post is saved to drafts, with a broken attachment and the alt text that I have carefully (sometimes) entered replaced with "This post contains an invalid attachment!" This can be especially frustrating when answering an ask, and when there are multiple images that had to be alt text tagged.
The attachments are not invalid, of course, they are just normal images. Generally speaking they upload normally and quickly on the second attempt.
It would be good if fewer posts get eaten, but if this is not possible due to the servers just permanently going through it or whatever, it would be good if the alt text was preserved so that work doesn't have to be duplicated.
I have a similar issue on my desktop PC. Windows 10, Firefox version 116.0 (64-bit). Practically with every attempted image upload, the upload stalls at "uploading..." and does not advance. Clicking out of the post window saves the post into drafts with the above mentioned error "This post contains an invalid attachment". The same image files can be uploaded without issue from my phone via Android Chrome, and from my work PC via Chrome (work PC is on the same network as my desktop).
It's happening to me again, though it hasn't happened in months. Just like yours, it's a Firefox-only problem.
Can confirm, I've been experiencing this quite a bit on PC (Firefox).
I'm seeing this as well, but from safari browser.
Also it ends up deleting my written image descriptions, and every time I have to write them over again I get a bit lazier with the alt text.