
Like most apps, uninstalling Firefox from an Apple computer is a simple matter of deleting the application file. OS X Yosemite doesn't have a complicated uninstall application. However, Firefox does have additional library files that aren't removed when you delete Firefox.app. Locating these files in Finder can be tricky, since they're stored in a hidden library folder, but Firefox's help menu can point you directly to these files.
Step 1

Launch Firefox and click the "Menu" icon in the upper-right corner. Click the "Help" icon at the bottom of the drop-down menu. Select "Troubleshooting Information" from the Help menu.
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Step 2

Click the "Show in Finder" button located beside Profile Folder in the Application Basics section, to open a Finder window with your Firefox profile folder selected.
Step 3

Click Finder's "Column View" icon at the top of the Finder window. In this view, your highlighted Firefox profile folder is inside a Profiles folder to the left, inside a Firefox folder to the left of that. Delete the "Firefox" folder by dragging it into the Trash in the Dock.
Step 4

Close all Firefox windows. Click "Applications" in the left menu of the Finder window. Delete the "Firefox" icon in the Applications folder by dragging it into Trash in the Dock.