Following Hiperlink with Multiple Profiles headache

(1) - I have set Firefox to open the profiles choosing window when it's opened.

Now, when I open a link from the im program sapo messenger (http://messenger.sapo.pt/), neither does Firefox open nor the profile choosing window appears and trying to open firefox.exe does not open Firefox. I have to end firefox.exe process in order to open Firefox correctly.

This does not happen and the link I clicked will be followed if I have at least one Firefox window opened. However, I think that when I click such an hyperlink Firefox should show me the profiles window and after I chose the profile, show the page the hyperlink referred to.

I have spoke to sapo messenger's support and they say Firefox is not handling the hiperlink from sapo messenger correctly and I guess they're right, because this only happens because my Firefox is set as referred in (1).