If you're playing on the browser, the issue is normal as the browser does not have access to your filesystem, and requires me to implement a specific solution (such as your text box solution), which I haven't done because I could not think of a use case where you would want to import saves in the browser version.
You should be able to import saves (even those exported from browser) if you play the executable version.
If that isn't possible from a Chromebook, I'll think about a solution.