Issue

• no license provided

Why is this an issue

• see choosealicense.com (a site by GitHub) on the effects of not providing a license
• this project seems built using files from firefox-csshacks by MrOtherGuy and is licensed under MLP-2.0 and forces you to publish relevant files under a specific license

Additional Notes

• as far as I understand you can license files not taken from firefox-csshacks under other compatible licenses, but see the github license summary and/or the MPL-2.0 FAQ for details
• See Github Docs pages Licensing a repository and Adding a license to a repository for further details
• this issue also applies to your other repo Vertical Tabs