Demandware says 30 of its clients booked more than $100 million in online sales in 2015, up from 22 a year earlier.
The retailers topped Internet Explorer and Firefox consistency tests last month.
Dell.com had the best consistency score for Internet Explorer testing among large retailers tested in February, says Compuware Gomez. Last month, the retailer had the most consistent Internet Explorer site loading time with a variation of 0.72 seconds. Overstock.com had the best Firefox consistency score at 0.75 seconds.
QVC.com (0.81 seconds) placed second in Internet Explorer tests. Apple.com (1.07) came in third, OfficeDepot.com fourth (1.18) and Staples.com (1.29) fifth.
In Firefox testing, LLBean.com came in second place behind Overstock.com with a deviation of 0.84 seconds. Apple.com trailed in third place (0.91) and was followed by QVC.com (0.99) and OfficeMax.com (1.07).
The average Internet Explorer consistency score among the 22 retailers measured in August was 1.69 seconds. The same group of retailers produced an average Firefox score of 1.60 seconds.
The consistency ratings take into account differences in the speed of web page delivery across multiple visits.
Click here for the full test results.