I'm trying to control solenoids (on and off control) via Arduino Uno with Node-Red and Firmata, but don't want to use the injection button as is demonstrated in most examples. What other nodes are capable of interfacing with arduino to control solenoids?
I assume you are using the node-red-node-arduino nodes to communicate with your Arduino using firmata? If so, then that's the right thing to be using, the question is how you trigger them.
You say you don't want to use the Inject nodes to trigger them. That's fine... you don't have to use them. They are a quick and convenient way of triggering a flow manually.
Node-RED has lots of ways of triggering flows. Give us some idea as to what sort of thing you want to do and we can help point you in the right direction.