Can I transfer stocks from a stock plan account or ESPP to Firstrade?

Yes. To transfer securities from a stock plan account to Firstrade, you would have to request a DTC transfer at the delivering firm. Please provide the below information to the delivering firm when initiating the transfer. 

Receiving firm name: Apex Clearing Corporation 
DTC No.: 0158 
Receiving account number: Your 8 digits Firstrade account number 
Receiving account name: Client’s full name 
Firstrade contact email address: transfer@firstrade.com