At the current time, the Extensions.GNOME.org (aka EGO) website only supports a small number of browsers via the GNOME Integration plugin using NPAPI as the backend. This project is to make it easier for anyone to use the website regardless of which browser they prefer.
GitHub: https://github.com/MichaelTunnell/ego-zip-downloads-userscript Help/Support: https://github.com/MichaelTunnell/ego-zip-downloads-userscript/issues Changelog: https://github.com/MichaelTunnell/ego-zip-downloads-userscript/blob/master/CHANGELOG.md
Demo & Installation Tutorial
How to Install GNOME Extensions from Zip files (this is for after you already have a Zip file)