Excerpt and Include macros display redundant vertical scrollbar in Firefox

Issue Summary

When marking an excerpt on a page using the Excerpt macro, or when using Excerpt include and page include macros, a secondary vertical scrollbar appears in Firefox:

This only occurs in Firefox.

Steps to Reproduce

1. Create a new page.
2. Add an Excerpt macro.
3. Add some text into the Excerpt macro.
4. Publish the page.

Expected Results

The content should be displayed without a secondary scrollbar.

Actual Results

Content inside of the include or page include macros have a secondary scrollbar instead of expanding to fit the page space.

Workaround

Currently, there is no known workaround for this behavior. A workaround will be added here when available