Now that Google has officially released Chrome 51 on Android, it’s reversed a change that came with Lollipop in 2014. That release of Android brought in the option to “Merge tabs and apps” which put open tabs in the app switcher instead of all in one process and was on by default. The only problem was that we disliked it from the start, and so did many others, who quickly disabled it. Now the option is gone altogether, and the old tab selecting option is back by default. As we noted in our Lollipop review, it’s just an easier way to keep track of tabs, and also makes it easier to scroll through any recently opened apps. If you don’t have the new version already, check Google Play for an update.
Source: Google Chrome Releases, Google Play