Chrome: Much like how FBPrivacy gives you more control over your Facebook Messenger's settings on jailbroken iOS devices, Facebook Chat Pro lets you control whether others can see if you read a message, change the notification pop-ups and enable sounds while typing.
Install the Chrome extension and Facebook Chat Pro's icon in the toolbar lets you disable notifications for 5, 10, 30 or 60 minutes with a click. The extended settings menu has many more options. You can prevent friends from seeing you have viewed a message, disable the "[Your name] is typing" message when you are writing, and apply a noir style with typewriter sounds. You can also set how many seconds a notification pop-up will stay visible for.
It's a handy extension to have if you use Facebook Messenger a lot, especially for the ability to disable notifications for short periods with a couple of clicks.