If you are developing extensions on FireFox on OS X, and are having trouble getting your extension to install or work, you can get some additional debug information from FireFox by starting it from the terminal.
On OS X, you can do that with the following command:
If you need to start the ProfileManager you can do it like so:
Note, you may need to change the path to point to where you installed the FireFox bundle.
Any debug or error information will then be sent to the terminal window, which can make it much easier to debug any problems that might arise.
You can find some additional tips on setting up your debug environment for extension development here.