> I did try Vivaldi, and it has some good things about it; however, it is not
> exactly free/libre, GNU/Linux, Richard-Stallman-approved.
Indeed. The team claims that although the code is not on a Free license (aside from Chromium 
modifications, which are BSD license), but it is openly available for inspection:

https://vivaldi.com/source/

> Vivaldi makes connections to gezillions of different IP addresses.
I would be guessing it queries external sites for data needed to provide functionality like ad 
blocking (it needs to regularly update the ad filters), etc. Firefox seems no better here, I 
think.

> Otherwise, have you considered other Mozilla-based browsers, such as Icecat
I haven't heard about Icecat. I will take a look.

> There is also PaleMoon, as well as a few others, and most of these preserve
> some of the old Mozilla features that we have missed.
I do have Palemoon, which I primarily use when I need to download huge files. Palemoon has the 
Flashgot plugin, which intergates with Trinity's KGet allowing to easily redirect links to TDE's 
download manager. It's a pity that when Firefox moved to Quantum it left behind so many good 
extensions that have not been replaced until now and most likely will never be replaced.

> I am sure you have your own reasons for choice of browser, so I will
> refrain from rants against proprietary or "non-free" software.
I do prefer my software open source and only go for closed source when there's really a 
significant difference in software quality.

Janek