LibreWolf is a custom version of Firefox, focused on privacy, security and freedom. It is kept up-to-date with the latest stable Firefox branch. It is available for most major GNU/Linux distros and also for Windows and MacOS.
In case you are not using a tiling window manager (like i3 or Awesome) you may want to disable “resistFingerprinting” for a more seamless usage. However for maximum privacy protection it is recommended to keep it enabled. More info here. It is also recommended to use medium mode in uBlock Origin, but it breaks functionality of some sites, so I decided to keep the default iBlock Origin settings.
You can disable or enable “resistFingerprinting” in LibreWolf's settings or directly in the config file. This is the content of my librewolf.overrides.cfg (I'm using a tiling WM most of the time, so resistFingerprinting is enabled, my WM adapts LibreWolf's window size automatically).
defaultPref("privacy.resistFingerprinting", enable);
defaultPref("privacy.clearOnShutdown.history", false);
defaultPref("privacy.clearOnShutdown.downloads", true);
pref("javascript.use_us_english_locale", false);
pref("intl.accept_languages", "cs, en, de, en-US");
You may want to use other language codes for accept_languages, of course. See LibreWolf config file for details about the cfg.
Sidenote: I do not recommend using Waterfox browser because its source code uses a very distinct (outdated) branch from Firefox, therefore it has security holes and also contains Google tracking code. Besides that it is a little bit more heavy on RAM and CPU compared to vanilla Firefox and LibreWolf (it's clearly missing some optimizations).
Mull is a great mobile browser, a privacy oriented and deblobbed web browser based on Mozilla technology. Available directly on F-Droid or after adding DivestOS official F-Droid repository (update 2024-10-27: the F-Droid repository has an outdated Mull version, use DivestOS repository).
If you are looking for more alternatives, check out the DivestOS page which contains a very good browser comparison table.