I managed to do it by pasting the link and clicking to post it BEFORE it expanded. Please go there and see what I spent ages reporting to you before the wretched nuisance of the '403 Forbidden' bug struck. 😠
Ah, ok. I'm using the latest Firefox on a Mac (the same issue is present on an older version of Chrome and an even older version of Safari). Looks like the software itself is SNAFU with respect to this particular thing.
