It's not like internet users have stopped searching for things online using Google, of course. Far from it.
Google's number of paid clicks surged 52 percent during the second quarter from a year earlier, helping drive online ad revenue to a market-leading $22.7 billion.
"People may spend more time on Facebook, but when they want to learn something, they still go to Google" apps, Kessler says.
Yet Google's cost per click—or what advertisers pay on average each time a user clicks on an ad served by Google —dropped 23 percent in the second quarter compared to a year ago, far more than Wall Street analysts expected.
That's because advertisers won't pay as much for smaller ads placed on tablets and smartphones as they will for larger ones for PCs.
Worse still, Alphabet CFO Ruth Porat said the shift to mobile means investors should get used to higher costs.
That helped send its shares down 3 percent after the report.
The average price of a Facebook ad, by sharp contrast, rose 24 percent year-over-year. Along with better-than-expected sales and profit and a reduced expense forecast, those results helped drive Facebook shares to record highs this week.
Mobile ad sales rose 53 percent year-over-year and now comprise 87 percent of Facebook's advertising revenue.
Facebook's core product is more suited to mobile advertising because the ads fit right into the main Facebook News Feed, in between status updates, news articles, home videos or whatever else people are sharing with one another.
So the broad shift to mobile web browsing has so far been better for Facebook's bottom line.
Other measures of growth in each company's second-quarter financial results show why Google might want to try to do more of what Facebook does.
Google does have a significant head start on Facebook in the market for mobile video ads, as its YouTube service now has 1.5 billion monthly users and lots of original content.
Facebook, meanwhile, is still figuring out what kinds of original video it wants to offer.
"If you could point to one area where Facebook hasn't yet fulfilled its promise, it's in video," says Kessler, who otherwise calls the company the best in the internet sector at delivering "consistent, strong growth across all measures."
In other words, not a bad company to imitate.