The reason you can't use the old version of the web-browser based release is because the new version overwrote the available Story Formats settings your web-browser's local storage cache, this overwriting occurs for each new version.
There is a technique you can use to allow access to the Story Formats settings of the older version, but it requires you to open the Application (*) section of your web-browser's built-in Development Tool and to manually delete the twine-formats related entries within Local Storage (*) cache. One this has been done simple closing and the reopening the web-application will result in those entries being recreated for the version of Twine 2 you are using.
(*) Depending on which web-browser you are using both of these items may have different names)