For the time being, I mostly use manual testing.

Most of the older browsers are covered by three VMs: Windows 95, Windows ME, and Windows NT 4.0.

Most Windows Netscape can run in Wine, so I can use symlinked .wine directories to switch versions.

I also do occasional testing at Best Buy or Walmart (many thanks to those places) at a cross-section of their available devices -- a couple of desktops, a couple of phones and tablets of each flavor, etc.

I also often ask people if I can test out my website with their device (or if they want to participate in a 5-minute user study)

For difficult things like Mac IE, I just have a couple of devices e.g. G4 Macs and iOS 7 iPad.

Of course, there are text-mode browsers, which I usually install with apt or whatever.

I also use online emulator services like BrowserStack, they have a pretty good slice in their free tier, and a couple of minutes is enough for smoke testing.

Also, I sometimes come across public devices, such as desktops in survival center, library, hotel, or public community space, and I test on those.

With my own devices, I test across various public wifi locations, so that I can provide workarounds for e.g. content blockers or inadequate proxying.

I use Charles Proxy locally to simulate low-bandwidth connections and other common issues.

I have also asked rare use-case users, such as visually impaired, to test using a script, usually through topical Facebook groups.

That's about all I can think of for now, there's probably more.