How To Install The Latest Firefox (Non-ESR) On Debian 10 Buster (Stable) Or Bullseye (Testing)

Debian Stable and Testing only have Firefox-ESR in their repositories. This article presents 2 ways of installing the latest non-ESR Firefox on Debian Stable (Buster) or Testing (Bullseye): installing it from the Debian Unstable repositories (with apt pinning and instructions to revert the changes in case you need it) or manually downloading and including Firefox in the applications menu.