recent versions of Firefox (with a few privacy add-ins) have become nearly unusable for me.
Due to performance issues? Mind that Linux is likely a good bit more usable on your hardware and you may very well not need to move away from Firefox after all.
“missing MSVCR120.dll” (part of Windows C++ Redistributable pkg)
Not sure, if you’re saying that you already found this out, but yeah, there is an installer from Microsoft for this Windows C++ Redistributable package.
bergerrealty.com & attheshore.com (web cam hosting sites)- “no compatible source was found for this media”
I’m on Linux and these work for me in Falkon. But it could be that your particular hardware + the Chrome browser engine that Falkon uses, results in no source being compatible (e.g. your graphics card only offers acceleration for the H.264 codec, which is what Firefox generally uses, not VP9, which is what Chrome/Falkon prefers). Then it would still not work after the switch, although again, Firefox would probably work…
legacy.com (obituary site) - various page loading and display issues. If I fully enable content permissions, I can get the home page displayed, but no links are functional.
Again, works for me. I didn’t have to do anything. I have the built-in ad block enabled, but no other customizations, as far as I remember (I only use Falkon as a backup browser).
facebook.com - Log-in successful. Home page displays, but is immediately followed by: “Qt Qtwebengineprocess has stopped working” here is the pertinent info from the Windows analysis pop-up:
I don’t use Facebook, so can’t test this one. This could be due to using the 32-bit version, but it’s really difficult to say. Only real pointer I can give you is that “QtWebEngine” is a thin wrapper around the browser engine of Chrome (which is called “Blink”). It’s part of the Qt GUI framework that Falkon uses. So, likely not specific to Falkon.
If you’ve got a spare USB stick, I would recommend just preparing it as the Linux Mint installation medium. You’ll be able to boot off of that into a largely functional Linux Mint system, without actually installing it.
This will be slower than a proper installation, as it will read the data off of the USB stick rather than your hard drive, and lots of these “live” installation medias do not come with all the media codecs, so this will probably not be representative for your webcam sites.
I’m also not entirely sure, if you can just install Falkon into that live system.
But at the very least, you can give Firefox a look (it’s the default browser), see how that performs, and just play around with the system.