The trend highlights two things: the explosive growth of mobile commerce overall, and the increasing importance of gatekeepers who can drive shoppers to apps.
It also reflects shifting consumer behavior.
"It makes sense," Goldberg wrote on his Betashop blog. "Fewer people are sitting around in front of computers on Thanksgiving day. Instead, they are with family, showing them their favorite apps on their phones and tablets."
Fab had previously been doing about 30 percent of its revenues through mobile, hitting 33 percent for a period in September.
Goldberg didn't give sales figures for Thanksgiving, but he's previously said he expects the company to do about $150 million in annual sales.
Fab was one of a handful of companies Facebook tapped to experiment with an advertising feature that encourages mobile users to download apps.
Apple's tweet, as well as its all-important App Store rankings and featured listings, shows that it, too, has the power to make or break apps.
Apps specifically optimized for mobile shopping and checkout seem to be key for making commerce work on smartphones and tablets. So app gatekeepers like Facebook, Amazon, and Apple will play a bigger role in e-commerce as this trend continues.
One area where Fab has struggled is signing up Android users. But that doesn't seem to have hurt its holiday sales, and it also seems to be an industrywide conundrum: Android device users are far less prone to spend online than iPhone or iPad users. That's a real headache for Google.
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