Although my inbuilt ad-blocker in Opera is set to 'on', I have discovered that when I loaded PPRuNe the 'switch' changed to 'off'.
Having clicked the shield to 'on' my ad-free PPRuNe browsing has returned.
I don't know what might have initiated the change - certainly not a conscious action by me.
Now I still have to work out why the inbuilt spell-checker doesn't work.