If you'd like to avoid association with no-extension-files don't get the file from the Download button. Click on the 'Files' tab in the menu and download the *_extonly.jar file instead.
If you are upgrading to a new version delete the old jar from the plugins folder, copy the new one, close eclipse, and then start it (from the command line) with the -clean option. E.g. '/home/koko/eclipse/eclipse -clean'. You have to start it like this only once.