Is there a clear difference between fibroblasts and myofibroblasts?

As far as I am concerned, there are certain markers to identify myofibroblasts. I am sure some cells are permanently myofibroblasts (e.g. in the mammary gland?), but can a regular fibroblast trans-differentiate to myofibroblast upon certain signals (e.g. mechanical stress)? Does a regular fibroblast have nice stress fibers with all components or only myofibroblasts have alpha-smooth muscle actin as a component of their stress fibers?

Thank you in advance for any input. 😉