Trello Card Checker от ReDa

Ever miss a deadline because you simply forgot to check?

This extension keeps track of your tasks and alerts you the moment something is overdue — so nothing slips through the cracks. It uses Trello as the underlying planning tool, making it easy to organise, schedule and stay on top of what matters.

Open the popup and everything you're late on is right there — no tab switching, no context loss.

What you can do from the popup:
• See all overdue tasks at a glance, with how many days past due
• Mark a task as done with one click
• Reschedule any task using a built-in calendar picker
• Archive tasks you no longer need
• Snooze alerts for 30 min, 1 h, 2 h or 4 h when you need focus time
• Create a new task dated for today without leaving the browser
• Switch between multiple boards instantly from the popup

Background behaviour:
• Checks automatically between 08:00 and 18:00
• Polling frequency is configurable from 1 to 60 minutes
• Settings sync across all your Firefox instances via Firefox Sync

Setup takes about 2 minutes — you just need a free Trello account and an API key from trello.com/app-key.