While using Atcoder, I noticed some features I needed were missing, so I developed an extension — Atcoder Companion ( Link for Chrome & Link for Firefox).
The extension offers the following features:
1. Adds a status column to the list of problems (inspired by Atcoder Color) 
Provides performance and rating predictions (inspired by ac-predictor)
Allows for downloading and copying test cases with ease.
By clicking on the extension icon, you can enable or disable certain features.
The extension's source code is currently messy, so I plan to publish it once I clean it up.
If you encounter any issues while using the extension, please let me know in the comments. Any feedback or ideas for new features are greatly appreciated.
Update 1: Add link for Firefox
Update 2: Source code is available on Github
Wonderful Work , I still have issue with Downloading Test Cases :(
_hoanglong_ please share the settings required for Chrome on windows , Thanks !
MathModel Could you tell me more details ?
UPD : Thanks _hoanglong_ , It seems that I must restart the system so it works !
Could you also upload it to the Microsoft Edge webstore or provide a crx?
I'd like to try it on Edge too :D