Files created on startup
From MozillaZine Knowledge Base
Mozilla applications store personal information in a profile folder. In Firefox and Thunderbird, as well as in SeaMonkey 2 (currently in Alpha testing), if you choose a custom location for your profile and select a folder that is not empty, files and folders belonging to the Mozilla profile will be added to that folder's contents. If you delete the Mozilla files and folders, they will be recreated the next time you use the application.
WARNING! Never create a new profile in a location that contains other valuable data, such as your Desktop or My Documents. Doing so may result in loss of all data in that location if you later delete the profile, as explained here and in the bug reports listed below.
For example, if you create a new Firefox profile and choose the Desktop as the folder location, you will see files and folders belonging to your Firefox profile, such as these, appearing on the desktop (other Firefox profile contents are listed here):
To resolve this problem you will need to use a different location for your Firefox or Thunderbird profile. Follow these steps carefully:
Related bug reports