The open-source developer first announced plans for a Windows 10 Firefox in early July, saying then only that the browser would launch "soon." In planning documents later that month, Mozilla pegged Firefox 40, which shipped today, or the follow-on Firefox 41, slated for release Sept. 21, as the likeliest candidates, with a heavy emphasis on the former.
Mozilla's decision to rush out Firefox for Windows 10 was a turnabout from 2014 when it abandoned years' worth of work on a browser for the touch-centric Windows 8.
The company recognized that it had to do something on Windows 10 to retain current Firefox users because Microsoft was aggressively promoting its own new browser, dubbed Edge, as the default for the OS. During the initial setup, Windows 10's "Express Settings" assigns Edge as the default, even if users had previously specified a rival like Mozilla's Firefox or Google's Chrome. Most users will simply click "Next" in the Express Setup without diving into the details.
Mozilla's CEO, Chris Beard, took exception to the tactic. In a letter Beard sent to Microsoft Chief Executive Satya Nadella, Beard blasted the default browser switch on Windows 7 or 8.1 PCs upgraded to Windows 10.
"These changes aren't unsettling to us because we're the organization that makes Firefox," Beard wrote. "They are unsettling because there are millions of users who love Windows and who are having their choices ignored, and because of the increased complexity put into everyone's way if and when they choose to make a choice different than what Microsoft prefers."
Microsoft defended the browser change but left the door ajar to modifications down the line.
Firefox for Windows 10 is actually little different from the stock version, which can run on the new OS as well as on older editions, including Windows 7.
Much of the emphasis Mozilla put on Firefox for Windows 10 today in a blog post was dedicated to pointing users to instructions for making the browser the default, booting Edge from the spot. "If you upgrade to Windows 10 or get a device that already has it installed, your default browser is set to Microsoft Edge by Windows, so we created support materials to show you how to restore or choose Firefox as your default browser in Windows 10," the blog explained.
Those instructions consisted of several steps, one of CEO Beard's complaints, that required the user to confirm they wanted Firefox as the default when it was first launched, then to make the unintuitive move to click on "Microsoft Edge" in the ensuing Settings pane to open a list of rivals before explicitly selecting Firefox.
A side effect of fixing Firefox as the default browser is that the search bar embedded in Windows 10's taskbar is also switched to Mozilla's pick for that market. In the U.S., for example, tapping Firefox as the default also changes the taskbar search from Microsoft's Bing default to Yahoo, Mozilla's domestic search provider partner since late last year.
Other changes in Firefox not limited to the Windows 10 version ranged from better detection of potentially malicious downloads, to the beginnings of an effort to crack down on dodgy add-ons. On the former, Mozilla continued to rely on Google's Safe Browsing API (application programming interface) to power its malware sniffer; the add-on campaign, just underway, will ultimately disable any add-on not certified and digitally signed by Mozilla.
Mozilla has to do whatever it can to hold onto its current user base, which has shrunk significantly in the last two years. As of the end of July, Firefox accounted for about 12% of the browsers used that month worldwide. A year prior, Firefox's user share stood at 15.5%; in mid-2013 it was 18.3%.
Firefox 40 for Windows 10 can be downloaded from Mozilla's website.