Note: the graph shows combined usage share of all versions of respective browsers, so it doesn't just show usage share of e.g. Firefox 3 and IE6 but Firefox 1-4 and IE 1-9.
As you can see, IE saw a rapid decline in usage share in Europe in the last year, obviously since lots of former IE users switched to using Chrome whereas Firefox users tended to continue using Firefox instead of switching over to Chrome. As a consequence of this, in November last year Firefox overtook IE in usage share and is still holding the #1 position. However, in the last three months Firefox's usage share seems to have started slowly falling as well. This is puzzling a bit, since Chrome's increase in usage share doesn't seem to have sped up. The biggest advantage Firefox had over IE seems to have been in March, when IE had 35.92% while Firefox had 37.12%. April is only halfway through but it's interesting to note that so far since last month:
- Chrome's usage share increased by 0.68%,
- IE's usage share decreased by 0.11%,
- Firefox's usage share decreased by 0.51%.
From those numbers, Chrome obviously seems to have started chipping away at Firefox's usage share more than it does at IE's usage share. Chrome's usage share seems to be increasing at a relatively constant rate for the last year (with the biggest increase being from November 2010 to December 2010, +1.49%). When you take a look at http://gs.statcounter.com/#browser-eu-monthly-200904-201104, besides noticing the "death of Opera", you will notice that Chrome's usage share seems to have grown "linearithmically" during the first year, while during the second year the increase in growth seems to have slowed down and the usage share is now increasing at a semi-linear rate.
The release of Firefox 4 doesn't seem to have had a serious effect on Firefox's usage share so far, but that can still change until the end of the month.
It will be interesting to see whether Chrome's increasing popularity will cause Firefox to fall back to second place, or will Firefox remain in front of IE until Chrome overtakes them both, or will the increase in Chrome's usage share slow down and/or stop and Firefox remain on the first place, or (my favourite outcome) will usage share of Chrome increase until it overtakes IE but stop then, leaving Firefox at #1, Chrome at #2 and IE at #3.