Recent advancement of mobile device technologies played a key role in increasing the user base, and a large number of people are using the device to gather information and browse the Internet. Web browsers are in the center of such activities. In this paper, we analyze the I/O characteristics of five popular web browsers: Chrome, Firefox, Opera, Dolphin, and UC. We chose a website that has 52 objects and 509KB as the sum of all the objects. After analyzing the ratio of read and write I/Os, we found that browsing is a write-intensive activity. Three of the browsers issued more than 50% of I/Os using fsync() and fdatasync(). About 50% of I/Os are for updating file system metadata and journal. The number of I/Os that a browser generates for SQLite and cache files is more than 50% at the lowest and 90% at the highest of the total I/O counts. In this paper, we define write amplification of web browsers to address the amount of extra I/Os browsers generate. We found that web browsers write on average of 11.7 times more data to the storage than the sum of original web contents.