Here's something which has annoyed me for 5 years or more but which I don't think I've ever reported.
In the writing room, when I click in a link field which is configured to expect a web link, the sidebar opens and focus is automatically given to the newly-revealed URL field. It shows
https:// and the cursor is blinking at the beginning. That means it's a placeholder, right? And anything I type will replace the placeholder?
I type the keystroke to paste. Of course I'm pasting -- URLs are long and error-prone. The URL appears, and the far right end of the field has the end of the URL I pasted. Looks good to me. I click "link to this page" or press enter.
I might or might not notice at this point that the URL has been set to
<the URL I pasted>https://. If I don't notice, the link is of course broken. If I did something silly when writing my site's code, it might even crash my website.
https:// was prefilled, not a placeholder, yet the cursor had been put at the beginning of the line. So after pasting, the cursor was at the far right, at the end of what I pasted, with the
https:// overflowing the right side, invisible to me.
So every time I fill in such a field, I have to remember to manually clear the field before pasting. Very bad UX.
Perhaps the intention was for the field to be focused but with the cursor at the end, so that I could immediately start typing the part of the URL which comes after the protocol? Well, in my opinion typing a URL by hand is not a use case that should be given much thought. As long as it's possible, no special accommodations should be made since it'll only be done for the shortest, most memorable URLs.
More likely, it's a bug, and it was intended to be a placeholder.
However, in my opinion it shouldn't have a placeholder at all, nor be prefilled with anything.
I use Firefox.