Could use an on/off toolbar button... Rated 5 out of 5 stars

The problem with this extension is that it also blocks the marking of messages as "read". So as long as it's on, messages in the inbox will forever be marked as "unread" which is really annoying. Of course in order to apply the "read" status, you can disable the add-on temporarily, click on the messages, then re-enable it, but that's very time consuming having to go to the add-ons manager every time etc.

A tool bar button for turning it on/off would save a lot of time in that case!

EDIT:
The developer now added an on/off button, making this the first extension of its kind for Firefox to finally offer this feature! I therefor updated my Rating from 4-stars to 5-stars! Very nice, thank you!

My only criticism is that the button *icon* is not very stylish. It has non-transparent white background, and the icon itself is too small. So maybe if in the future you could address that as well it would improve the add-on even more! :)

This review is for a previous version of the add-on (v1.1). 

Thanks for reply

I added on/off feature in new version.

Here is link to download new version of addon: https://addons.mozilla.org/firefox/downloads/file/186810/facebook_chat_seen_notification_remover-v1.1.rev124-fx.xpi