[svisser]

I don't think you know enough to take action. You might draw incorrect conclusions from what you saw and it may have unwanted results if you raise this with a project manager (or him).

Usually there are other signs as well when an employee is looking to leave (search online). When those confirm your suspicion you could consider talking about it. But from just a few open browser tabs I don't think you can draw conclusions (it may well have been recruiter spam that looked curious).