I had had to upload an upgrade to Firepower Management Center over a lossy VPN connection where HTTP uploads were failing. I ended up using Filezlla and depending on resume to get the upgrade uploaded to the system. I just thought I'd share the process in case someone else ran into this.
So, just pop in the IP address of Firepower Management Center into Filezilla or whatever SFTP client you like - sftp://a.b.c.d, port 22, and login as admin.
You will be dropped into /Volume/home/admin, where you'll have permission to upload the upgrade file into. When the file is done uploading, SSH into FPMC and run this command:
sudo mv /Volume/home/admin/*.tar /usr/local/sf/updates/
Enter the admin password again when prompted.
Now, refresh the updates page and your upgrade will be there!
