As the second major tech site to experience widespread downtime today, Facebook appears to be recovering from an outage that has lasted for more than an hour. Early into the interruption, users believed the problem pertained to a DNS issue. Although the main site (facebook.com) wouldn't resolve for millions of users, subdomains such as m.facebook.com, touch.facebook.com and beta.facebook.com loaded fine.
Although a purported member of Anonymous quickly took credit for causing outage, Facebook has since chalked the issue up to a botched traffic optimization test and not nefarious deeds. As part of its tinkering, the company made a DNS-related change and that resulted in many users being misrouted. The company says that the largest downtime occurred in Western Europe, but that Facebook should be fully operational now.
As of writing, the site seems to be loading normally on my end, though some folks are reporting that images are missing from the site, suggesting that its content delivering network (CDN) may also be suffering issues. If the site still isn't working for you and you're uninterested in accessing the service through one of its subdomains, one user has uploaded instructions on tweaking your hosts file to access the main site.
Earlier today, Google experienced intermittent issues across several of its services, including Gmail. Although Gmail outages aren't particularly uncommon, many users (not least of which is Search Engine Land's Danny Sullivan) have reported that Google's problems were also causing Chrome to crash, presumably because it's tightly bound to logged-in Google accounts for cloud syncing among other less-kosher reasons.