Yes - you need a complete update - you wouldn't want just the plugin if it needed a fix that was in the rest of GitHub and not in the e.g. rc2 version you downloaded and installed.
In simple terms, select the Joomla3 branch in GitHub, download the zip file and unpack, then upload the administrator, components, libraries, media, modules and plugins directories to the Joomla root directory of your web site (which will already have these directories in there) - overwrite existing files where they exist. Then go to Extensions / Manage, search for Fabrik, select all and click Refresh Cache, then to Extensions / Discover click Discover then install, then clear your server Joomla cache and your browser cache. And Robert's your parent's sibling.
As for the close button, I agree that in the back-end administrator screens it would make sense to have a close button on View Details - and since you only get the List dropdown in Back-End and not in the front-end, there is already code you can add to. However, adding this is not a priority for me, and probably not a priority for Fabrikar staff, but if you want to add it yourself, please go ahead. (That said, looking at the URLs and how the Close button is in the Joomla Toolbar, it looks like the View Details screen is structurally different from the View Data screen, so this may not be that easy.)
S