I didn't think it was a fact, but it worked for me. I get Vbucks for Fortnite for a 30-second survey.

To get Vbucks, complete the survey here

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This works as described for me when pasting a video URL into an incognito browser window with the added period. In addition to removing pre-roll ads, it also eliminates mid-roll interruptions for videos as well. By the time you’ve copied, pasted, and altered the video URL, I’m not sure how much time you’re really saving over just waiting for the “skip ad” button to appear — but it does indeed work.

As for why something so trivial is successfully getting around YouTube’s advertising machine, here’s what Redditor unicorn4sale said when posting the trick:

It’s a commonly forgotten edge case, websites forget to normalize the hostname, the content is still served, but there’s no hostname match on the browser so no cookies and broken CORS - and lots of bigger sites use a different domain to serve ads/media with a whitelist that doesn’t contain the extra dot

With over 4,000 upvotes on Reddit, it’s likely that YouTube already knows people have caught wind of this loophole. The oversight is probably going be corrected sooner rather than later.