[Clytie]

Thanks to both Forrest and Jonathon for their helpful replies. :)

I'm glad this very useful feature hasn't disappeared entirely: it's just disappeared from where I expected it to be!

I tried all three suggestions on the Quick Reply box for this forum post, and both the contextual menu Zoom command and the new button on the Status Bar provided the larger input window, which is great.

There was no drag icon in the lower RH corner of the window, nor did dragging there do anything, but I think that is because the Quick Reply box already has resize arrows of its own, in the top RH corner.

I'm most relieved that I now have access to the larger input field again. Thankyou!