Although other factors may have contributed to the decline in IE's user share, the simplest explanation is the upgrade directive. By demanding that users switch from, say, IE 8 to IE11, Microsoft opened the door to alternatives: If users knew they had to change browsers, they seem to have been much more likely to select a non-IE browser, like Chrome, than if Microsoft had let sleeping dogs lie and not forced an upgrade.
Chrome has been the biggest beneficiary of Microsoft's must-upgrade-IE rule. In the 13 months since Microsoft mandated IE upgrades, Chrome has gained a whopping 10.3 percentage points, ending September with a user share of 29.9%, its highest ever. Unless Chrome's advance unexpectedly stalls, it will pass the 30% milestone this month.
Most of Chrome's gains came from IE, but a bit more than a third originated from Firefox, which lost 3.8 percentage points in the same 13-month span. In September, Firefox's user share stood at 11.5%, the lowest since August 2006.
In other words, Microsoft handed a golden opportunity to Google by requiring IE users to upgrade.
The debut of Edge, a browser that runs only on Windows 10, has not helped. (Net Applications lumps in Edge with IE editions to come up with the Internet Explorer total, which was 51.6% last month.)
Although Edge accounted for 2.4% of all browser user share in September, up slightly from 2% in August, its growth appears to have come at the expense of IE11, not Chrome or Firefox. IE11 fell by 1.6 percentage points last month: Part of that decline was probably due to those who upgraded from Windows 7 or 8.1 -- both which used IE11 as their default Microsoft browser -- to Windows 10, and then switched to Edge.
Another part of IE11's slide was likely due to deserters to Chrome, with some of those users eschewing Edge for Google's browser when they switched to Windows 10. That was evident in another statistic: In September, Edge was run by 36% of Windows 10 users, down from August's 39%.
Browser share is not just about bragging rights; it has a financial impact. Each browser maker tries to steer its users to a different search provider, where customers, and thus the user share, can be monetized through search result advertisements. IE and Edge, of course, default to Microsoft's own Bing search engine; Chrome defaults to Google; and Firefox, at least in North America, to Yahoo.
A shrinking share of IE could translate into fewer searches on Bing, with a concurrent decline in ad revenue.
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