Can you be fired while out on workers’ comp?

Yes, you can be terminated on worker's compensation. Worker's compensation provides--as the term implies--compensation for your injury; it does *not* hold or guaranty your job. An employer has to make "reasonable accommodations" for an injured employee, but a reasonable accommodation is one that still lets the employee do the core or important functions of his or her job. If the employee cannot do the core or important functions of his or her job, he or she may be terminated--the law does not make employers retain people who cannot or will not work. And "light duty" is not a reasonable accommodation--the employer is not required to let you out of the important (or all!) functions of your job, or create a new set of duties for you: you must be able to, even if it is with some minor change in rules or some not-too-expensive assistive device (i.e. a reasonable accommodation), do your job.
If you cannot work due to an injury, you could miss work without being terminated if you have enough paid time off (PTO) for your absence. Or if the employer is covered by the Family and Medical Leave Act (FMLA), which means has at least 50 employees within a 75 mile radius, and you are eligible for FMLA (worked there at least a year; worked at least 1,250 hours in the last 12 months), you could take up 12 weeks of unpaid FMLA leave.
But without using PTO or FMLA, if you can't work, you may be terminated, and worker's compensation will not preserve your job.