Mozilla's Nicolas Nethercote, the developer in charge of the MemShrink project, called that kind of leak a "zombie compartment." According to Nethercote, zombies accounted for 90% of the identified add-on leaks.

In a last month, Nethercote trumpeted the new leak prevention code, citing one example where Firefox 15 used just 24% as much memory as Firefox 14 after tabs engaged by an add-on were closed.

"We are confident that Firefox 15 fixes the vast majority of add-on memory leaks, and that as a result, many users will see drastic improvements in Firefox's performance and stability," said Nethercote.

According to Web measurement company Net Applications, Firefox users accounted for 20.2% of all those who went online last month. Irish measurement firm StatCounter, meanwhile, pegged Firefox's global share for July at 23.7%.

Windows, Mac and Linux editions of can be downloaded manually from Mozilla's site. Installed copies will be upgraded automatically.