Problem solved. :)
I cleared my cache, but that wasn't it....
Turns out I'd totally forgotten that I'd 'ZOOMED IN' on some pages on my computer a couple of days ago....and this was what had 'cut off' the 2 buttons at the bottom of the 'Insert/edit image' box! However, I decided to 'Maximize' the box after a while of staring mystified at it....and there were the 'INSERT' and 'CANCEL' buttons....
Then it dawned on me, lol.