Environment: Moodle User at moodle.stfx.ca
Purpose: Guide of how to fix collaborate not automatically opening a new window/tab
Online Classroom
Accessing your Collaborate Online Classroom is usually done by simply clicking on the activity link in your Moodle Course:
This normally will open up a tab and the Collaborate Lobby for your course: 
However, at times you may see that clicking leads instead to:
This page is unexpected and may cause confusion as to how to enter the Collaborate Lobby/Online Class.
If this happens and you want to enter the Online Classroom, simply click on the "Open in new window" link and this should open a new tab/window with the Collaborate Lobby for your class.
To fix the issue. With Editing On, click on "Edit" and then "Edit Settings" from the menu to the right of the Online Classroom link
Once in the "Edit Settings" page, simply go to the bottom and Save and Return to Course: 