Emptying the Browser Cache

The browser cache serves as a buffer for the Internet pages you visit. The browser stores resources such as page content and images in case you open the website later. For example, large-format images or recurring page elements such as stylesheets do not have to be reloaded from the web when a new page is created. This approach reduces the data volume and speeds up the page build-up.

However, the cache only fully leverages these advantages if it is static, and if the website has not been updated on the server in the meantime. Dynamic content changes every time it is called, which means cached data is always obsolete.

By default, Firefox automatically organizes the cache; the default size is 350MB (Figure 6). If necessary, you can disable automatic cache management and limit the cache size. Clicking on Clear Now causes Firefox to remove all traces from the hard disk. Alternatively, you can just delete the data from the past few hours in the menu using Library |History| Clear recent history.

Figure 6: The cache's size can be limited in the Firefox settings.

Deleting Form Data

Firefox remembers everything you type in input fields on the web, such as your name and email address when you subscribe to a newsletter or your address when you order from an online shop. If you are concerned about data privacy, you can delete this data in the menu under Library | History | Clear recent history. In the window that then appears (Figure 7), select the desired period of time, click Details, and check Form & Search History.

Figure 7: Deleting form data and other user-specific data in the History menu.

Blocking and Filtering

In order to reduce the risk of attacks via the web browser, it helps to suppress additional JavaScript code. Popular Firefox add-ons for suppressing scripts include NoScript [2] and uMatrix [3]. Ad blockers such as uBlock Origin [4] ensure that the browser only loads what you want it to load. Firefox also lets you surf in a private window (New private window), in which Firefox does not remember cookies or form data.

Another option is to lock the web browser into a secure environment, such as a virtual machine. At first glance, this approach might seem complicated, but it definitely slows down attackers, and it typically doesn't have a noticeable affect on performance given the capabilities of today's hardware. In Firefox 57, the browser now outsources many tasks to a sandbox that runs separately from the rest of the system [5], which reduces the importance of running the browser in a virtual machine.