A year after it pulled the plug on silent updates in Firefox 4, Mozilla said it will debut most of the behind-the-scenes feature by early next year.

Assuming Mozilla pulls off silent upgrading this time around, it would make Firefox only the second browser to take that route. Google's Chrome has been the poster boy for automatic updates that remove the user from the equation and can't be switched off.

Mozilla did not say it was copying Chrome -- it's denied doing so with other features -- but the chairman of the Mozilla Foundation, Mitchell Baker, acknowledged what she called "update fatigue."

"In the past we have been very careful to make sure people know something is changing with their Web browser before it changes," said Baker, who heads the non-profit organization that oversees the Firefox-making Mozilla Corp. "Today people are telling us -- loudly -- that the notifications are irritating and that a silent update process is important."

The difference between then and now, a Mozilla developer explained, is the rapid release schedule that upgrades Firefox every six weeks.

"Most users don't want to think about software updates nor version numbers and now they are being forced to do so every six weeks," said Brian Bondy, a Mozilla developer working on one component of silent updating, in a blog post last Friday.

According to Bondy and other information published on the Mozilla website, the current goal for most of the multi-part project is Firefox 10, slated to ship Jan. 31, 2012. Some pieces will appear in earlier and later editions, however.

When Firefox receives the feature, the browser will download the upgrade in the background, then install it the next time Firefox is restarted. Users will be reminded to install the upgrade 12 hours later if they haven't restarted the browser before then.

Mozilla may sidestep the UAC (user account control) prompts in Windows Vista and Windows 7 by building its own Windows service for the silent upgrade mechanism. That will require users to okay the install one time only; all subsequent upgrades will not bother the user, said Bondy.

That's a different tactic than the one used by Google's Chrome, which avoids UAC prompts by installing itself into a different folder than "Program Files" on Windows.

Unlike Chrome, Firefox will let users switch off silent upgrading.

Mozilla began work on a security-patch-only silent update service for Firefox 4 in August 2010, but quickly abandoned the feature. Firefox 4, which launched in March 2011, was delayed several months as developers wrestled with numerous problems; that delay was one reason why Mozilla shifted Firefox to a faster release cadence.

Some of that work, however, was clearly recycled in the new project.

Last year, Mozilla developer Robert Strong had rejected the idea of mimicking Chrome to avoid UAC prompts, saying that Google's approach was risky. "Chrome accomplishes [silent updates] in part by forcing the install of Chrome into the user's profile which has a set of issues associated with it that we don't want to have, so we aren't taking that route," Strong said at the time.

Strong leads the Mozilla team that's again working on silent upgrading.

Even without a silent upgrade mechanism, Mozilla has been pulling most users along with each new edition. According to Web metrics firm Net Applications, Firefox 6 -- which launched mid-August -- made up over half of all copies of the browser in use last month. The "tail" of those still running Firefox 4 and Firefox 5 was relatively short, representing about 13% of all Mozilla browsers.

More information about Mozilla's silent updating plans can be found on the company's website.