I had a look at the debug console (Shift-Ctrl-Alt-D), and saw that it's getting net::ERR_FILE_NOT_FOUND. The URI it's trying to access is:
I clicked on the link in the debug console output, and got a blank file in the "Sources" tab of the Developer Tools window.
So I went to look in /tmp/.org.chromium.FiFgpj/storyformats/Harlowe and I found a file called "format.js", but not a file called "format.js?callback=storyFormat&_=14447959245114".
This is a regression relative to the 64-bit Linux build of Twine 2.0.8, which finds its story formats just fine running on the same computer.
The application is using a URL to open the story format file (format.js), the question mark in the URL indicates that there are parameters (eg. callback=storyFormat&_=14447959245114) to be pass to the format.js file once it has been opened in the application's built-in HTML render. (think custom web-browser)
Interestingly, if I manually tell Twine to open the unpacked story formats in /tmp/.org.chromium.Chromium.randomletters/storyformats/name/format.js with the "Add a New Format" button of the Formats dialog, it works fine.