Open the Library folder for your Mac user account:
(OS X 10.6 or previous) Click the Finder icon in the dock. Your home folder will be selected, (usually the name of your Mac user account). In the right side of the window, click the Library folder to open it.
(OS X 10.7 or above) Click the Finder icon in the dock. On the menu bar, click the Go menu, hold down the option or alt key and select Library. A window will open containing your Library folder.
Open the "Application Support" folder, then open the "Firefox" folder, and then the "Profiles" folder.
Open the folder with “default” in the name to open your profile.