Font and image size are customizable in many browsers. This allows you to increase the viewing size of your mailbox, Contacts or Cloud, for example.
To zoom in or out on the website view, hold down the Ctrl key on your keyboard and press + or -.
To set the original size of the website, hold down the Ctrl key on your keyboard and press the 0 (zero) key.
Mac keyboards do not have the Ctrl key. Instead, use the ⌘ key (command key).
You can find additional information on the help sites of each browser: