Zero methodology or explanation for how this conclusion was drawn.

That's why Dig Deeper and Spyware Watchdog are better sources. Although, you could use mitmproxy to check browsers listed in the Shadow Wiki, but it doesn't seem to work, at least for me, and I did try Windows 7, Trisquel, Xubuntu, Salix... maybe it actually doesn't work or I just can't install things with pip.

I use old version of Pale Moon and Chromium for websites requiring a newer browser. Both seems ok.