This tutorials shows how to remove seen from Facebook chat. Everyone who uses Facebook know's that they have feature, that tells you when other side have seen your message. And it  works both ways: Other side sees when you have read their messages. I have good news for you, if you don't want that other side know's when you have or have not seen their messages. You can remove this "seen" notification with browser extensions. There is couple of things that you have to know before installing

When Unseen extension is installed, then your Facebook works like this:
1. You send chat message to recipient -> You can't see when message is read
2. Recipient sends chat message to you -> Recipient can't see when you have read it
3. You have new message on Facebook inbox and you open it -> Message will stay as unread state!!

Installing Unseen to Chrome

1. Go to FB unseen installation page by clicking this.

2. Click Add to Chrome

3. Confirm installation by clicking Add.

4. Extension is now installed!

If you ever have to, you can disable unseen extension by clicking unseen icon from Chrome.

 Installing Unseen add-on to Firefox

1. Go to Unseen installation page by clicking this. From there click Add to Firefox.

2. Click Install Now.

3. Add-on is now installed!

If you ever have to, you can disable this add-on. For some reason Firefox doesn't have this neat disable/enable button near address bar, so you have to do this hard way.

1. Click Firefox from top left corner and from there click Add-ons.

2. Select Extensions from left panel.

3. Click Disable where you can see Unseen.

As i earlier stated, if you have enabled any of these extensions, then your inbox messages stays as unread state. It's the annoyance that comes with these. Facebook shows that you have 10 new messages in inbox, but when you open it, it's just same old messages.