There are many reasons why you may want to install Firefox on a Chromebook (could be for security, privacy or just as a technical challenge). You could install the Android app but that isn’t a full featured browser. Here are the instructions on how to install it in the Linux container.
Go to Settings
Search for Linux and Turn it On.
You will get the installation window. Continue and let it complete.
You will then be presented with the terminal window, run an update then an upgrade.
Install Firefox on ChromeOS
Now we are ready to install Firefox.
Got to the terminal and enter sudo apt install firefox-esr
Now you can start Firefox by entering the firefox-esr command to invoke the app.
If you want to invoke Firefox-Esr but also need your terminal to work (at the same time), use the command firefox-esr &