I am very embarrassed to report that I have found the cause of the apparent malfunction to be due to me. I have been working on configuration of this computer over several days and one part of this is to set up firejail, so that the machine can run sandboxed. Seemingly, I had an instance of Vivaldi still running in this mode whilst I used another incarnation when I tried to collect extensions. I apologise profoundly for my stupid error and can only hope I have not caused too much inconvenience to other users.
I discovered my error yesterday evening but I have been unable to post from Vivaldi, even though Blockers and my VPN are disabled.. I can log on to this forum and see the thread but at about this time, your system reports that connection has been lost. When I log out, the Forum reports that I cannot be validated. I have tried to reach the forum several times this morning, without success. I am now using Firefox and this is working perfectly. I cannot offer any explanation since yesterday, I could post from Vivaldi , even though I was in the error condition reported above.
Best regards to all,