Well according to the graph it isn't so much firefox growing more IE shrinking, which means other browsers are taking up the shrinkage.
So another statistic being able to be manipulated as firefox is only just beginning to get back to where it was percentage wise in July 2009 and still not as high as it was in following 6 months.
Perhaps that graph title should be IE to make history by dropping off top browser spot in Europe as it isn't so much firefox winning it but IE losing it.