"Windows uses the Local and LocalLow folders for application data that does not roam with the user. Usually this data is either machine specific or too large to roam. The AppData\Local folder in Windows Vista is the same as the Documents and Settings\username\Local Settings\Application Data folder in Windows XP.
Windows uses the Roaming folder for application specific data, such as custom dictionaries, which are machine independent and should roam with the user profile. The AppData\Roaming folder in Windows Vista is the same as the Documents and Settings\username\Application Data folder in Windows XP."
and
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Roaming
is the folder that would be synchronized with a server if you logged into a domain with a roaming profile (enabling you to log into any computer in a domain and access your favorites, documents, etc. Firefox stores its information here, so you could even have the same bookmarks between computers with a roaming profile.Local
is the folder that is specific to that computer - any information here would not be synchronized with a server. This folder is equivalent in XP to C:\Documents and Settings\User\Local Settings\Application Data.LocalLow
is the same folder as local, but has a lower integrity level. IE8, for example, can only write to the locallow folder (when protected mode is on)."