@kiziuk: See the solution from alexs to my identical query above.

@alexs: Thank you! All is well again. Much appreciated the advice.

Opera 85.0.4341.28 on Linux is not saving its window geometry when closing. The application always starts the same size centred on screen so if you close the browser maximized, for example, it doesn't open maximized next time Opera is started. Not a deal breaker but a lot of users enjoy Opera opening with the same window geometry when it was last closed.

The best browser by far for everybody, novice to expert.

I believe that this add-on harbours adware. When I used it flashtalking.com kept trying to aquire data from me even after I had blocked access to that domain locally. This indicated to me that the Avast add-on was trying to contact that advertiser, repeatedly, from within my browser so I removed it. Since it has been removed I never saw any activity viz., flashtalking.com again. You do the math.