Most Firefox 4 users updated to Firefox 5 in the first week, although the turnover speed was slower than when Chrome last shifted editions, Web usage data showed.
Mozilla released Firefox 5 , the first update under the rapid-release scheme that aims to issue a new version every six weeks, on June 21.
In the week since then, Firefox 4's usage share dropped from 16% to 7.2%, according to data from Irish analytics company StatCounter, representing a decline of 55%. During that same period, Firefox 5's share climbed from half a percentage point to 10%, indicating that the new version picked up the decline of Firefox 4, and more.
As part of its new release program, Mozilla changed the way that it offered updates. Although it hasn't yet mimicked Chrome, which silently updates in the background, Firefox went from an "opt-in" approach for major upgrades to an "opt-out" strategy identical to what was previously used solely for security updates.
The change seems to be working.
But Firefox's pace was less dramatic than Chrome's most recent upgrade, StatCounter's statistics showed.
Chrome 11's share plummeted from 17% to 2.7% in the first seven days after it was replaced by Chrome 12 on June 7, a drop of about 84% in usage. Meanwhile, Chrome 12's share shot up from seven-tenths of a percentage point to 15.5% in the same time frame.
Other Firefox editions, such as Firefox 3.6, stayed flat during the same seven days that Firefox 5 rose and Firefox 4 fell, another clue that the latter's opt-out update offer, which Firefox 3.6 lacks, efficiently moved users to the next edition.
Mozilla has been criticized by corporate customers and rival Microsoft over the new faster-paced release schedule, and the ensuing retirement of Firefox 4 from support. Others have simply been confused by the quick turnover from Firefox 4 -- which debuted just three months ago -- to Firefox 5.
By Tuesday, Mozilla appeared to have heard the calls for help from enterprises.
Without making any promises, a Mozilla executive today said the company would look into how it might assist companies that rely on Firefox.
Noting that enterprises need to test a browser upgrade before deploying it to their workers, Jay Sullivan, vice president of products at Mozilla, used a blog post to announce, "We are exploring solutions that balance [enterprise] needs, with active discussion in our community, including valuable input from IBM."
An IBM manager who said he managed 500,000 copies of Firefox in the company -- which adopted the open-source browser last summer -- has been vocal about the demise of support for Firefox 4, calling it a "kick in the stomach."