Do firefighters need to have excellent vision in ontario?

yes................................

I would think first responders would need to have at least decent vision. To see through smoke, to see injuries to help treat them properly, for driving to emergencies, etc.

Glasses would likely interfere with safety requirements.

When a vision requirement is needed for a job, often times corrected vision is acceptable in this. I would think, in this case, prescription contacts would be acceptable. However, different places may have different views on this.