It was just over ten years ago that Google entered the browser market with Chrome, which was positively received for its speed. To celebrate the occasion, Google shared a special birthday tweet over the weekend, featuring a birthday cake and a teaser for a surprise coming on September 4.
Over the past ten years, Google's browser has grown to conquer the majority of the browser market, holding over 60% of the market share according to NetMarketShare. Like most browsers, Chrome is free to use, but some might say that it pays for itself thanks to all the user data it feeds back to Google, which is why they might prefer a browser like Mozilla's privacy-focused Firefox. With that being said, the Mountain View giant is open about tracking browsing habits to make improvements to the browser.
As to what surprise Google might be preparing for tomorrow, all we know is that this is the planned release date for Chrome 69. The surprise could be related to the major redesign which can already be enabled if you feel like tinkering with the browser's settings, or it could just be some sort of Easter egg to celebrate the occasion. For now, your guess is as good as ours.