Microsoft has invited the Firefox guys up to Redmond to test Firefox and Thunderbird on Vista to ensure compat­i­bility. The move isn’t entirely unexpected, after all, Firefox has been steadily eating into Internet Explorer’s market share ever since it was released.

It isn’t a wholly benev­olent move, however. Microsoft is making sure all the big appli­ca­tions run smoothly on Vista because if they don’t, people won’t upgrade from XP. Microsoft is seeking out big devel­opers now in a big effort to get all the major programs tested.

Previ­ously Microsoft had focused exlusively on commercial devel­opers but Sam Ramji, Director of the Open Source Software Lab at Microsoft posted on the mozilla.dev.planning newsgroup in an effort to get the ball rolling.