Hey, look at this!
For the record, overnight updates included Firefox 46.0.1 and Chromium 50.0.2661.102.
Now I'll post this, then try to edit it.
EDIT1: Hey, it looks as expected.
Hoping this was a fix, rather than an intermittent thing as others have referred to.
EDIT2: Oh poo! Looks like it's either intermittent or related to post size. Just tried to edit the other post. Nada. (See screenshot.)
Then I can come and edit here. Strange. Well, good luck with fixing it!