cloud Sync solution for xml File - required for Firefox Add-On called Internote

Freelancer Project: File Synchronization of up to five XML Files on five computers we will use this Firefox Add-On: [login to view URL] . We aim to use the same Notes on the same webpages. Therefore we need to sync our five referring XML files. For further in depth explanation please see : [login to view URL] I can see two alternative ways to reach this: either all five users directly work on the same remote XML (only one XML involved) But for that solution the Path must be Redirected to that remote location which I was until today unable to do! OR, alternatively, the second solution would involve to Sync those five xml-files in order for them to become alike. Some computers will be Mac, some Windows-based. But all the involved five computers will all use Firefox-Browsers and all use the same add-on (which will store the socalled "notes" within an xml-file)