Firejail is a SUID sandbox program that reduces the risk of security breaches by restricting the running environment of untrusted applications using Linux namespaces, seccomp-bpf and Linux capabilities.
I use it when running Thunderbird or Palemoon.
For that matter, I'll add
Palemoon itself.
Pale Moon is an Open Source, Firefox-based web browser available for Microsoft Windows, Android and Linux (with other operating systems in development), focusing on efficiency and ease of use.