CuLipSum oleh Fridtha

While there is demo material, the main point is that there's also a place to upload your own content via text file upload from your own machine or via copy/paste into the input page.

WARNING: Custom content will not be saved IF you delete or reload the extension, so save your content separately. Since there is a way to upload text files, you'll be able to reload your content easily if you save your content to a txt file first.
The first line of a text file will default to the title (but can be changed before you save), and the second line will be the tagline (also able to be changed before save).