Backfire is over 8 years old now, and is no longer maintained or actively supported. It is known to have multiple security vulnerabilities in the kernel and application software.
Assuming your device has sufficient flash and RAM to run a release that has updated security patches and support, upgrading to 18.06.1 would be by first suggestion.
If your device is no longer supported, there are many devices with sufficient flash, RAM, and support for current wireless protocols available for US $20-40.
Once you have either updated your firmware or moved to another device, make sure you run opkg update before you try to install packages.
Edit
https://openwrt.org/toh/us.robotics/usr9108
shows that it is a 4 MB Flash, 16 MB RAM, 256 MHz Broadcom BCM6348 device.
I would be very surprised if you can run much more that routing and wireless on the device.