Differences in shared workers across browsers

Question

I've tried to write simple web application using shared web workers. Everything worked as i expected in Chrome (55.0) and Opera (45.0), but when i tried to test app in Firefox i saw a little bit different behavior. In Chrome worker dies after closing last tab that was using it, but in Firefox (54.0 (64-bit)) it dies after closing last tab from given domain. So here's the question: is there any standard how browsers should behave? Cause in the end i don't understand is there problem or is it ok to get such different results.