I really like the Virtualbox vSRX compare to the QEMU version because the Virtualbox vSRX is so much faster compare to the QEMU one. We are talking about a lot faster.
Anyways, once you have the vSRX .vmdk, .vdi or .ovf file, all you have to do is import the file to Virtualbox. If the .vmdk is greyed out, convert the file into .ovf or .vdi; therefore Virtualbox can read it. To do so, navigate to File > Import Appliance then follow the prompt.
The VM is pretty much configured already, the only thing you need to modify is its name to your desire name, and network adapters. The network adapters should be configured in Paravirtualized Network and should be set to Not Attached in Virtualbox.
Import the VM to GNS3 by going to GNS3 > Preferences > Virtualbox > Virtualbox VMs > New. By default (at least from v1.3.7 and earlier version) the network adapter in GNS3 is in e1000. This adapter need to be changed to Paravirtualized Network (virtio-net). Click the VM that is in question in GNS3 then click Edit > Networks > then select the Paravirtualized Network (virtio-net). The reason being why we need to change the adapter is if the interface is using e1000, the VM won’t be able to reply back to any dynamips IOS, QEMU, VPCS and IOUs. You can increase the number of adapters as well. I believe the max is 6, but I could be wrong.
In GNS3 the RAM is set to 1024 MB; ensure the RAM is set to 2048 otherwise you won’t be able to see ge-0/0/* interfaces. This is done under Edit window.
These are optional, but they are pretty useful, tick Enable remote console, so that you can open a console window from GNS3. Also, tick Start the VM in headless mode. With this enabled, you can start the VM in GNS3 by pressing the Play button, and no Virtualbox window will pop-up.
Hope you will find this useful