2 thoughts with this:
* maybe a min-width could make it possible to see the cursor?
* maybe file a gecko bug with a simple testcase, I think the cursor should always be visible.

I've seen similar issues too, see for example https://bugzilla.mozilla.org/show_bug.cgi?id=942742, so it would be nice to see this fixed at the Gecko level.

When you file the bug please add the bug number here. Also, please put the comment besides the property so that a reader knows it applies to this property only :)