On Debian reboot after making these changes. It will save your time and avoid issues.
If you haven’t already discovered the wonders of sshfs, you really should start using it — it’ll probably shave hours of your day as a web developer. Every now and then I come across the following problem when first installing sshfs and have to take a moment to think about the problem, so I’ve decided to post it up here to help anyone else and as a reminder to my forgetful self.
Problem:
fusermount: failed to open /dev/fuse: Permission denied
Solution:
usermod -aG fuse <your-username>
exec su -l $USER
Depending on your setup you may need to prefix the solution commands with sudo although this isn’t specific to any platform and many user su. You may not need to reboot but it could save you some hassle in the long run if the problem still persists. It’s common sense but just in case you didn’t get it, replace <your-username> with the username you use.
Creds: http://www.elfnet.org/2010/06/29/sshfs-failed-to-open-devfuse-permission-denied/