I think it is just that. I live in Melbourne myself, and while I'm not involved in the gay scene, I'm also not that far removed from it. What you've got here is a bland statement saying "we're boycotting this product" without actually stating any changes made. Does the council even use Mozilla's stuff? If they do, what changes are they making?
How effective have previous campaigns of theirs been? (Like I say, I'm admittedly not involved in the scene, but I haven't actually heard the name of the aids council for literally years). How much political reach do they have to make people actually change the web browser they're using? Few people use thunderbird or firefox OS or Mozilla's other subsidiary products.
And what is the basis of their claim? A single sizeable donation from six years ago. What more recent evidence do we have that he's still acting this way? People can and do change over the course of years.
This announcement is merely jumping on a political bandwagon, and the suggested boycott has no teeth in it. It's a robotic response, and smacks of the usual way these things are written: responding to the hot gossip with no further investigation. Fine, boycott away if they want to, I'm just saying that press releases like this - giving little insight, having no real teeth, no course of action, and which can be written in 10 minutes - don't require much to trigger them. It doesn't even mention that Mozilla's primary product is Firefox and you can start off by using something else!