In undergrad, we mainly called the professors "Dr X" - lab instructors and tutorial leaders (who were usually grad students) were called by their first.
In grad school most of the younger professors and the sessionals were called by their first name. Certain senior professors were still called Dr X - mainly the eldest and most distinguished, who came from the previous generation.
Now that I have a PhD, it's usually a first name basis, although at my current institute senior Japanese professors revert to "X-san", which feels more comfortable. More junior Japanese are called by first names by non-Japanese colleagues, but I've noticed that Japanese colleagues follow Japanese standards (X-san for pretty much everyone senior and on the same level, but last names are used for juniors too, with some variations I haven't grasped completely, like X-kun for a junior male colleague).
If I'm referring to someone else, it's usually by first and last name - like "John Smith is coming to give a colloquium" not "Dr Smith is giving a colloquium" unless they're known personally by both me and the person I'm speaking too.
As an aside - referring to your instructor as "Professor X" by default is not a safe option. In the university structure, the term Professor refers to a particular type of position and rank. Your instructor may be a professor, but they may also be a Dr but not a professor (sessionals, post-docs, short term staff), or a Mr/Ms (graduate student, someone with a Masters but not a PhD). Calling a grad student teaching a class is "Professor" like calling a first year undergrad "Dr Jones". They might get there someday, but it's a long way away.