e10s is not enabled on Linux (and probably OS X) by default in ESR 52 based nightlies
For some reason e10s is not enabled on Linux (and probably OS X) in ESR 52 based nightlies. Both our extensions and HTTPS-Everywhere + NoScript set multiprocessCompatible to true, so I wonder what is going on.
To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information