Firefox in Ubuntu by default comes with something known as “desktop integration” . What this does is provide a way to link Unity interface with popular websites like Facebook, Gmail, Twitter and so on.
This however can be annoying because browsing any of these websites through Firefox will result in a pop-up asking whether to allow integration or not.
Here is how  to turn off these Ubuntu web apps integration notifications in Firefox:
Go to Edit > Preferences.
From the “General” tab, uncheck the option ” Prompt integration options for any website”. If you wish, you might want to keep a few exceptions by clicking the “Exceptions” tab and adding list of websites for which integration is still needed.
All done. From now on, say goodbye to those prompts that kept popping up before.
Happy browsing.