I want to access the cookies of a website opened in a specific tab through the firefox-addon-sdk.
Sorry, for the general question, I'm not able to find anything on the web about it.
Is someone able to give a hint?
You can use the tabs module to get to the tab and attach a content script to it to do as you please (such as accessing cookies). See the section "Run Scripts in a Tab" or, for more, the tutorial it references: https://addons.mozilla.org/en-US/developers/docs/sdk/latest/dev-guide/tutorials/modifying-web-pages-tab.html