How to see a list of all installed Firefox extensions and export it?

Extension List Dumper is an addon that can save your addons and themes as a file.

Edit: As of Firefox 30, the above addon no longer works. You can get a list of all installed addons and other information about your Firefox installation by entering about:support in the URL bar. You can also try Addon List Dumper (restartless) instead if you want to easily export a list.

If you want to automate this, here's a Python script that prints the names of the installed addons, including an enabled flag. It accepts a single argument, the Firefox profile path, which can be found in the about:support page.

import json, os, sys
PROFILE, = sys.argv[1:]
path = os.path.join(PROFILE, 'extensions.json')
data = json.load(open(path, encoding='utf-8'))
for addon in data['addons']:
    enabled = '*' if addon['active'] else ' '
    name = addon['defaultLocale']['name']
    print(enabled, name)