A little Script for https://bugzilla.opensuse.org/show_bug.cgi?id=1174184

fix78.py

#!/usr/bin/env python3
# (c) 2020 Wonko21 
# Public Domain, No rights reserved.

# A little Script for https://bugzilla.opensuse.org/show_bug.cgi?id=1174184#c21
# Inspired by https://gist.github.com/kaefer3000/73febe1eec898cd50ce4de1af79a332a


import lz4.block
import sys
import json

def fix_lpack(lpack):
    if not lpack['path'].endswith('.xpi'):
        print('Adding .xpi to path')
        lpack['path'] += '.xpi'
    if not lpack['rootURI'].startswith('jar:'):
        print('Prepending jar: to rootUri')
        lpack['rootURI'] = 'jar:'+lpack['rootURI']
    if not lpack['rootURI'].endswith('.xpi!'):
         print('Adding .xpi! to rootURI')
         lpack['rootURI'] += '.xpi!'

with open('addonStartup.json.lz4', "r+b") as lz4file:
    if lz4file.read(8) != b"mozLz40\0":
        print('Not an Mozilla lz4 file', file=sys.stderr)
        sys.exit(2)
    data = json.loads(lz4.block.decompress(lz4file.read()))
    for addon in data['app-global']['addons']:
        if addon.startswith('langpack'):
            fix_lpack(data['app-global']['addons'][addon])
    lz4file.seek(0,0)
    lz4file.write(b"mozLz40\0")
    lz4file.write(lz4.block.compress(bytearray(json.dumps(data),'utf-8')))

Thank you for your program, it fixed exactly the problem I had!
One thing to note, although all my addons were still showing enabled, they weren't actually running. For each one, I had to disable it and then enable it again in the About:addons page.

This was on OpenSuSE Tumbleweed 20200819 and Firefox 79.0.