FicTracker by Ro

AO3 is incredible for hosting fanfiction, but it has no native reading tracker. FicTracker fills that gap.
The extension adds a small floating panel to every AO3 work page. From there you can add the fic to your FicTracker library, set your reading status (To Read, Reading, Completed, On Hold, Dropped), and advance your chapter progress with − and + controls. When you reach the final chapter it automatically marks the fic complete. Your progress syncs to your FicTracker dashboard, so "Continue Ch. 5 on AO3" deep-links you straight back to the right chapter.
The panel has three modes — full, mini (a compact status bar in the corner), and hidden — and remembers your preference. On mobile it defaults to mini so it stays out of the way while you read.
FicTracker account required. Free at fictracker.app — the web dashboard is where you browse your full library, see reading stats and analytics, get AI-powered recommendations, and track WIP updates.
Permissions used:

Storage: saves your login session locally so you stay signed in across page loads
archiveofourown.org access: reads work metadata (title, authors, tags, chapter count) from AO3 pages you visit, and runs the tracking panel on work pages