The 9gag post filter is a Firefox extension designed to enhance user interactions on the 9gag platform by restoring lost functionalities and providing advanced filtering options. Key features include the ability to bring back downvotes, mark spam accounts, and display the number of days a user has been active next to their username on every post. Additionally, users can hide posts from users with less than a specified number of days, anonymous accounts, and those with blue checkmarks.

This subscription-based add-on is specifically built for social and communication purposes, particularly aimed at blog-like interactions on 9gag. It also allows filtering posts by specific tags or keywords in the title, giving users greater control over their feed. The extension is compatible with Firefox on Android, making it accessible for mobile users, and it is open source, allowing for community contributions.