Wi-Fi Sign-in impossible with enabled Add-on
If you connect to public Wi-Fi, you often have to accept their terms of use which are stored in a local (router) website. To access this site you can open a tab with an equivalent URL. HTTPS Everywhere tries to grab the SSL Certificate from the server which is not accessible at this moment so an error occurred and the page fails to load. This can be manually fixed by simply deactivating the Add-on for the time while you accept the hoster terms.
To upload designs, you'll need to enable LFS and have admin enable hashed storage. More information