This extension connects to SocialBlade to fetch latest sub-counts for PewDiePie's channel and T-series' channel. It then displays the difference in the badge-text and displays more detailed counts in the popup menu of the extension.
The extension is open-source: github repository

Install

• License: GNU General Public License v3.0 or later
• Weekly downloads: 0
• Average daily users: 0
• Rating: 5/5 of 1 ratings
• Created: 2019-04-02 19:14:12
• Last updated: 2019-04-02 19:20:07
• Homepage:
• Support site and email
• Orig: https://addons.mozilla.org/en-US/firefox/addon/pewdiepie-vs-t-series/
• API: {733fa85a-6bbd-4cf2-8692-28185e90beaa}