What: Shares of Criteo SA (ADR) (NASDAQ:CRTO) fell as much as 13.2% Thursday afternoon, then partially recovered to trade down 7% as of 3:30 p.m. following a Financial Times report highlighting impending new ad-blocking features to be incorporated into Apple's (NASDAQ:AAPL) mobile Safari browser.

So what: Specifically, Financial Times notes the new tool "would block advertising and associated tracking technologies on the iPhone's browser for the first time." It's hard to quantify exactly how popular such an extension would be when it eventually rolls out, but it seems clear it would not be to Criteo's benefit. After all, Criteo gave significant credit for last quarter's strong results to traction in mobile, with 84% of clients using its multi-screen advertising solution.

Now what: At the same time, however, ad-blockers are hardly new to the industry. So it's hardly a guarantee that Criteo's business will suffer meaningfully, even given a new ad blocker from the likes of Apple on its massively popular mobile platform. In the end, while this is definitely something to keep an eye on going forward, I don't think Criteo investors should be running for the hills just yet.