The extension requires access to the github.com, gitlab.com and bitbucket.org domains (access browser tabs for Firefox) in order to read the repo URL and provide its intended functionality. This information is not collected or transmitted in any way. You can always control which sites the extension has access to via your browser settings.
Source code is available on GitHub (Click here for Safari version) if you want to take a look at how the extension works. Should you have any questions regarding this policy, please email [email protected]