Update preview.gif in README to showcase Firefox

[0scvr]

Description of Changes

Updated the preview.gif in README file to showcase Firefox instead of Jellyfin.

Issue Ticket Number and Link

See #62

Review Checklist

• [x] I have included the issue I am fixing by adding #IssueNumber.
• [x] Added a GIF or screenshot (if applicable).
• [x] Provided additional information (optional).

[biplobsd]

@0scvr Awesome gif. Thank you very much, contributed to the OneClickRun. Have a great Hacktoberfest!