Every quarter since the end of 2011, slightly more consumers have been signing into retail web sites with their Facebook credentials than with their other social identities, according to Janrain, a provider of social media login technology for 400,000 web sites. In the first quarter of this year, 57% of consumers logging into Janrain’s retail clients’ sites did so through Facebook, compared with 55% in Q4 and up from about 43% in Q1 2012, it says. Janrain lets web sites visitors create accounts and sign in to e-retailer sites by using their already established log ins with such sites as Google, Yahoo and Facebook.

Janrain has clients in retail, media, entertainment, consumer brands, technology and nonprofits and education. The company declines to say exactly how many of its clients are in retail, but says the retail-specific findings come from a sample of several dozen web sites.

Shoppers’ preference to log into retail sites through Facebook “opens up for retailers a number of interesting personalization opportunities,” says Michael Olson, product marketing manager at Janrain. That’s because consumers tend to include more detailed personal information in their Facebook profiles, such as their Likes and interests, compared with what they share on other social networks, he says. So, when they log in to a retail site through Facebook and chose to share those details, the retailer can customize the products it shows them better than it could with, for example, only demographic information.

Because Facebook users’ data are often much richer than data from other social networks, some e-retailers that offer multiple types of social logins highlight the Facebook option above all others, Olson says. Janrain customer Sears Holdings Corp., for example, displays a much larger Facebook login button above ones for Yahoo, Google, AOL, LinkedIn and Twitter. A small question mark button next to it explains to customers in a pop-up window the benefits of signing in via Facebook: they’ll be able to find Facebook friends on Sears.com, receive personalized group and product recommendations, see friends’ upcoming birthdays while browsing the site and have the option to share their shopping activity on the social network.

After Facebook, 28% of consumers in Q1 logged into retailers’ web sites with their Google Inc. identities, 7% with Yahoo Inc., 2% with Twitter, 1% with AOL, 1% with Microsoft and 4% with other credentials, such as LinkedIn, Janrain says

 “We all have different identities across different types of sites,” Olson says. Consumers may use their LinkedIn profiles as their professional identities, for example, perhaps saving Facebook for their off-the-job needs, like shopping. However, he says, “While Facebook is slightly increasing in popularity over the past quarters, there is a strong segment of consumers that prefer to check out and register on retail web sites using a different existing I.D.” Google, for one, has a notably large share of retail web site logins, he says. “I don’t think we’ll ever see one social network I.D. take over completely.”