Online consumers in the United States spent approximately $41.9 billion in the third quarter, 15.4% more than the $36.3 billion spent in the third quarter of 2011, comScore Inc. reported today.

That growth represents the 12^th consecutive quarter of year-over-year growth for e-commerce spending, as well as the eighth consecutive quarter of double-digit growth, the web measurement firm says. In the second quarter of 2012, e-commerce spending increased 15.0% to more than $43.15 billion, comScore said in August.

The recent spending figure bodes well for the rest of the year, says comScore chairman Gian Fulgoni. “Such performance offers some optimism as we approach the holiday season, especially given recent improvements in consumer sentiment,” he says; comScore says that 48% of consumers rate the economy as “poor,” which is eight percentage points better than in the second quarter. “With the housing market beginning to show signs of recovery in addition to increasing,  if still underwhelming,  job growth, there appears to be strong enough footing to support a very healthy online holiday shopping season.”

Last month, Shop.org—the e-commerce arm of the National Retail Federation trade group—predicted that online retail sales will increase 12% over last year’s holiday shopping season and reach between $92 and $96 billion.

In its report today, comScore says that spending in the following product categories each increased at least 16% in the third quarter compared with the same period a year ago: digital content and subscriptions; consumer electronics; event tickets; apparel and accessories; and computer Software.

ComScore also says that its latest quarterly survey shows that 37% of U.S. consumers have used smartphones while inside stores to check prices or to even purchase a product online—a behavior commonly called “showrooming.” Over the last two quarters, that figure has increased by five percentage points, comScore says.