When using Internet Explorer or edge, it's impossible to create or edit a Web scenario. When update or Add is pressed, the Steps created for the scenario are lost and an errors is displayed:

–Field "Steps" is mandatory.

In provided example, the scenario was created from Firefox with an existing Step:

Then, if opened from Internet Explorer and Update is pressed, I see this:

As seen in the screenshot, the existing step was removed.
The same problems happens if a new Step is added from IE, it is removed when Update/Add is pressed