I have Librewolf installed now. Use the flatpak.
I suggest everyone really concerned about privacy try Mullvad. It has some pretty cool features. One note is that. like any browser, you compromise anti-fingerprinting by adding extensions. the problem with Mullvad is that, given the small pool of users, you will stick out like a sore thumb by even adding one extension. Mullvad is intended to be used "as is".
Regardless, here are the instructions for installing Mullvad on Solus, Good as of last week:
Create a folder in Downloads or wherever and go into it from the terminal:
cd ~/.local/share && wget https://mullvad.net/en/download/browser/linux64/latest -O mullvad-browser.tar.xz
tar -xvf mullvad-browser.tar.xz mullvad-browser
rm mullvad-browser.tar.xz && cd mullvad-browser
./start-mullvad-browser.desktop --register-app
A couple of additional niggles:
Currently, I don't think you can set Mullvad as the default browser. There is an issue on the github
I don't know how the Mullvad extension works if you don't have Mullvad VPN.
P.S. And as mentioned above, I don't use it as I don't need this level of security and I find Brave easier.