Same problem. It started yesterday and Shopify has reskined their interface again today. I started a discussion thread yesterday and they was plenty of folks having the same problem. Both FireFox and Chrome on PC cannot print from within the Shopify interface.
Live Chat help support yesterday was no help. The reported the .dev team ran no updates. Which is clearly a lie.
I'm stunned there was no testing for issues across browsers before updating. I'm hoping Shopify reads these discussions.