Nowadays the Web and Web browsers have become the most important and universal platform for people to search, view, process, and exchange various kinds of information. Consequently, today's users usually open many Web pages simultaneously in order to perform multiple tasks in parallel, which makes Web browsers crucial in our daily task management. However, no existing Web browser provides users with sufficient support for the management of many tabs or windows of opened pages. On the other hand, wide displays have become more affordable and prevalent, while extra space on those displays is not utilized effectively in Web browsing. In this paper, we propose a new Web browser interface aiming to support efficient task management in Web browsing on wide displays. In order to help users switch between opened Web pages, we show thumbnails of the pages in the extra space around the currently focused page. In the page thumbnails, we emphasize distinctive elements in each page in order to make the selection of the thumbnails easier. In addition, we calculate the relevance between pages based on users' switching history, and emphasize pages relevant to the current page by adjusting the size or opacity of the thumbnails. This further helps users find the thumbnails of needed pages, and also helps users get the overview of the page set related to the current task.