Save the expanded/collapsed state of each folder regardless of browser or resolution.

The suggestion "Collapse folders as the default view" may be officially "Completed" but it is still lacking. Mobile is not the only resolution would benefit from this.

As a user commented in that suggestion, the folder state should remain just as the user left it.

As another commented, it is annoying to collapse them all down first.

Do you prefer to have your folders collapsed by default?