If you have your product categories-vocabulary in a menu, Drupal Commerce can't by default activate the active-trail when viewing a product node. This can be bad UX, since user has to remember from which category he came to the current product.
Answer to this problem is Taxonomy Menu Trails-module. It sets the active-trail on nodes if you have that node's terms in the menu.
Here's basic instructions how to get it working with Commerce.
- Enable the module
- Edit the Content type you want to enable this function for (in case of Commerce, edit the product display: Structure -> Content Types -> Product Display
- Under Taxonomy menu trails-tab, check the vocabularies you want to use. Check the other settings if necessary
- Hit Save