Properly packaging Firefox extensions

On Windows 

run this from a command prompt

cd myexample 

zip -r ../myexample.xpi * 

cd ..

ls *.xpi

On Mac OSX

run this from a shell in Terminal

*Exclude the hidden .DS_Store files

cd example

zip -r ../example.xpi * -x "*.DS_Store"

For more information see 

https://developer.mozilla.org/en-US/Add-ons