Sorry realised that was vague but unable to edit. Deleted this: Profile: /Users/my user name/Library/Application Support/com.operasoftware.Opera
but browser isn't really working again sufficiently: the few sites I use Opera for are either not rendering correctly, or reverting to a white screen as previously reported (same in private window), so stopped using this browser for now and reverting to an old Safari.
Ridiculously, can't update Safari due to running Mac OS 10.8.5, so I have to put up with the mobile verion of Twitter among othr things. But that's another story. Will invest more time into researching any other possible browsers sometime, or may just have to have a windows PC running at the same time to view some sites.