Thousands of Firefox cookie databases containing sensitive data are available upon request from GitHub repositories. This data can potentially be used to hijack authenticated sessions. The cookies.sqlite databases are usually found in the Firefox profiles folder. They are used to store cookies between browsing sessions. They can be found by searching on GitHub with specific query parameters.
The situation is quite piquant due to the fact that using these cookies you can log into other people's accounts without entering a username and password. A number of cookies are specially designed to temporarily store authorization data, which saves users from having to enter the same data every time they visit certain websites.
By leaking text cookies, hackers can easily and very quickly log into someone else's accounts and change their passwords. It is possible that these are important Internet resources such as online banks, social networks, etc. Hackers can use this information for all sorts of shenanigans on behalf of ordinary users, as well as for blackmailing their owners.
The incident greatly alarmed security experts, who recommend that Firefox users change all passwords as soon as possible.
A source: theregister