Microsoft's new Edge browser is being used by a minority of those running Windows 10 -- between one-sixth and one-third -- according to data from a pair of analytics vendors.

The early returns on Edge not only hint at Microsoft's failure to get the earliest adopters to rely on the new browser, but also question Mozilla's contention that Windows 10's setup will result in defections from its own Firefox, or by association, other non-Microsoft browsers.

During July, Edge accounted for just 0.14% of all browsers tracked by California-based Net Applications. With Windows 10's user share standing at 0.39% for July -- and because Edge works only on Windows 10 -- the browser was run by about 36% of its potential users (0.14% divided by 0.39%).

Net Applications measures user share using visitor tallies to its customers' websites. The result is a rough estimate of the percentage of the world's online users who run a specific browser.

Data from StatCounter, an Irish metrics vendor, also showed that Edge was far from the universal browser of choice among people who have upgraded to Windows 10.

Over the first 16 days of August, Edge's global average daily usage share was 0.7%, far below the 4.4% average daily share of Windows 10. In other words, StatCounter pegged Edge as accounting for about 16% of the online activity of all Windows 10 owners.

Unlike Net Applications, StatCounter estimates usage share by tallying page views, generating a signal of activity rather than users.

It was impossible to determine which browsers were run on Windows 10 in place of Edge, as neither Net Applications or StatCounter break out their public data on browsers by operating system. The fractions that may have run Google's Chrome on Windows 10, for example, were masked by the fact that the browser also operates on more widespread operating systems, such as Microsoft's Windows 7 or even Apple's OS X.

(Again, the only reason why Edge's portion of the Windows 10 user base can be calculated is because Edge is exclusive to Windows 10. In the same way, the portion of Mac owners who run Safari, a browser exclusive to OS X on personal computers, can be estimated. Net Applications put Safari's user share at 5.1%, compared to OS X's 7.7%, meaning that about 66% of all Mac users run Safari as their primary browser.)

The low percentages of Windows 10 users currently running Edge signaled that Microsoft has not made its case for the new browser, at least among those who have jumped on the OS and its free upgrade. That's troubling, since Microsoft has positioned Edge as its browser of the future, and put in considerable effort to making it more compliant with standards, while relegating Internet Explorer (IE) in general, IE11 specifically, to a legacy support position.

At the same time, Edge's weakness counters Mozilla's assertion that because Windows 10 adopts the browser as the OS's default -- even if another had been set as the default on Windows 7 or 8.1 prior to upgrading to 10 -- Microsoft is unfairly leveraging its dominance in the desktop operating system market.

In a letter last month to Microsoft CEO Satya Nadella, Mozilla's chief executive, Chris Beard, slammed the switch to Edge. "The update experience [of Windows 10] appears to have been designed to throw away the choice your customers have made about the Internet experience they want, and replace it with the Internet experience Microsoft wants them to have," Beard wrote.

Mozilla published the letter to Nadella on its website July 30, a day after Microsoft began distributing Windows 10.

But the data from Net Applications and StatCounter show that the change to Edge promoted through Windows 10's Express Setup process has not resulted in a wholesale replacement of rival browsers.

That's not to say Beard's concerns were unfounded, either for Firefox specifically or non-Microsoft browsers in general. And it's entirely possible that Edge's user or usage share will grow as a percentage of the comparable statistics for Windows 10.

Yet the latest numbers from StatCounter -- which, again, measure activity, not users per se -- aren't encouraging for Microsoft and Edge. Since Aug. 1, Edge's share of Windows 10 has slipped, not snowballed as might be anticipated as the OS's user base accumulated more mainstream users and presumably tilted away from enthusiasts and power users who could be expected to retain their prior browsers.

In the past seven days' of StatCounter data, Edge activity accounted for 15.4% of Windows 10 activity overall, down from 16.6% during the seven days before that.