The browser extension works on big journals and we are working to add more titles all the time. To keep up with this fast approach of updating the extension and getting you updates to new site layouts we have had to make a choice. We found that the review time for the extension was going to become weeks at a time as we had "access" to all websites. The review team on Chrome found this to be a security risk. To keep the updates of the extension quick and review process short we have added all approved sites to an "allow list". This allow list means the extension will work only on publishers we specify out of the box.
We have a lot of requests for websites and of course we want to fully support a website before adding it to the list. With that being said we have added a new function to the extension. If you click on the extension on any webpage that has a PDF or use the shortcut key ctrl cmd + shift + s (on Mac) we will try and inject the "Save PDF to ReadCube" blue button. This should allow you to get PDFs from any website.
A demo of this is below. Let us know if you have problems by emailing us at support@papersapp.com.