"It was time to tackle the next big source of memory leak: poorly written add-ons," said Dotzler.
Although engineers worked with some add-on developers one-on-one, Mozilla could not scale that effort. Instead, it crafted a leak-prevention mechanism that blocked the most common kind of add-on memory mistake, in which the extra copies of a website aren't released after a tab has closed.
"These pages pile up, and can eat massive amounts of memory for no user benefit. They leak," Dotzler said.
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 post to his own blog 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 Firefox 15 can be downloaded manually from Mozilla's site. Installed copies will be upgraded automatically.
The next version of Firefox is scheduled to ship Oct. 9.
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