How do you erase files off your mac?

Drag them to your trash and click empty trash :D

If it’s applications I’d use AppZapper at appzapper.com

Mac apps tuck away files in some places like your ~/Library/Application Support and ~/Library/Preferences folder.

I see that TaoSan just suggested AppZapper while I typing. I use AppZapper too.

First of all: useless applications like firefox?

Second: Best way is to look at the install/uninstall manual for the specific program. As JP above mentioned, some applications create support files. But usually in the program’s readme.txt file it will say where to find them and delete them.

also there is a free alternative to appzapper called appcleaner.

Move items into your trash and open trash and click on empty trash for a simple clean. Also for a better trash clean open up your trash click on “Finder” at the top right of the screen and click “Secure Empty Trash.” Also all the applications listed by @lunabean and @TaoSan. Plus something I use appdelete which was free at one point.

Most of the support files installed by many applications will have no effect on your system unless the application is running. You can probably ignore them. The exceptions are those files that load themselves as startup processes, which you’ll find in /Library/LaunchDaemons, /Library/StartupItems, /System/LaunchDaemons and System/StartupItems. You have to be careful about the stuff in /System. If it was installed by the OS, and not your 3rd party app, and you trash it, you’ll be screwed.

If you do want to do a thorough cleaning and you don’t have an installer log, Pacifist will tell you the contents of an installer’s package. If the app is installed using Apple’s Installer, you can open it in Installer and choose File>Show Files.