@leocg
Thank you for replying
I found them. They were buried quite far in.
This, though, led to the next problem, and that is that Opera cannot open a large bookmark folder without crashing. (I right-clicked on the folder and asked Opera to 'Open All Bookmarks in Tabs' or something like that). Opera works on this for quite a while and then crashes.
I guess this should be a new and separate post, which I'll plan to make.