Mozilla is preparing nearly-silent upgrades to get customers stuck on older versions of Firefox onto the newest edition, according to notes on the company's website and its bug-tracking database.

The plan is to start upgrading older Windows editions beginning with the next stable release, Firefox 30, which is slated to ship June 10.

"In the next weeks we will [be] implementing a project to get users on older versions of Firefox back onto the latest version," said Benjamin Smedberg on a Mozilla developers planning discussion thread last week. "We've confirmed ... that about 2% of Firefox profiles are getting 'stuck' on older versions in each release cycle, at least back to Firefox 22."

On his LinkedIn profile, Smedberg identifies himself as a Mozilla engineering manager.

Smedberg said that Mozilla didn't know why some of its users continue to run outdated versions of Firefox. But with Firefox's background update mechanism, those users had to have explicitly switched off or at least restricted updates.

Older versions of Firefox are riskier to run, as the browser is regularly patched to close security holes. And the laggards, inadvertently or not, fragment the browser's user base, making it difficult for Mozilla and add-on developers to craft new features or extensions because they cannot expect all to benefit.

Mozilla plans a two-pronged approach to the problem. For users still running 2010's Firefox 3.6 (or versions even earlier), the company will suppress the usual add-on compatibility check, which may spook users into declining.

For those running Firefox 11 or later, Mozilla will deploy an "add-on hotfix," a feature that lets the firm push silent changes to the browser rather than distribute a full update.

In turn, the add-on hotfix pushed to Firefox 11 and later will trigger an update process to migrate the browser to the newest available. That process is still under discussion, according to a Bugzilla entry. Bugzilla is the Firefox bug- and change-tracking database.

Currently, Mozilla is considering two ways to drag Firefox users to the newest browser. One would silently download the latter in the background, then upon the next Firefox launch, display only the generic Windows UAC (User Account Control) prompt. If the user clicks "Yes" -- the almost-automatic reflex of most Windows users -- the new version will open rather than the old.

Clicking "No" on the UAC prompt will instead open Firefox as usual, then download the new version in the background while the user browses. Eventually, a tab will open asking the user whether they want to run the new Firefox. Clicking "Not now" at that point simply postpones the inevitable, as Firefox will continue nagging the user once each week.