Twitter Reveals Mozilla Firefox Cached Private Data

Mozilla Firefox Logo

Twitter announced last week that the way Mozilla Firefox stores cached data may have resulted in private information being stored in the browser’s cache. The information is stored in Firefox’s cache for seven days. People using other browsers were not affected by the issue.

Why was the Information Stored?

Data caching is mostly used to improve the functionality of a web page. The browser cache is a temporary storage location for files that are used to display a website. It stores the files so that your computer does not have to get them from a remote server, which would make a site function more slowly.

Firefox’s cache stored private files shared via direct messages and data downloads. Your data is vulnerable there. Hackers have tools that are specifically used to find information in browser caches. Obviously they are hoping to find sensitive information. Anyone who used Twitter’s direct messaging service or downloaded data from Twitter might had their data out to be taken by others. If a Twitter user logged on to their account using a shared or public computer, they have put themselves at risk. Luckily, Firefox does clear its cache automatically once information has been there for seven days. So private information that has been stored accidentally will have been deleted after a week.

Clear Cache

Twitter has confirmed that other browsers have not been impacted by this issue. Why was Firefox the only one who was? Because every browser behaves slightly differenty than the other. Only Firefox cached the data with the way that Twitter had their site set up. Twitter implemented Changes so that Mozilla Firefox no longer stores Twitter data in the cache. Twitter also gave the advice that “if you use, or have used, a public or shared computer to access Twitter, we encourage you to clear the browser cache before logging out, and to be cautious about the personal information you download on a computer that other people use”.

To clear Mozilla Firefox’s cache you go to “options”, click “privacy and security”, select “cookies and site data”, and choose “clear data”. There you uncheck “cookies and site data” and only select “cached web content”. Once you’ve done that you can click the “clear” button.

Cybersecurity analyst
David is a cyber security analyst and one of the founders of Interested in the "digital identity" phenomenon, with special attention to the right to privacy and protection of personal data.