Writing to an SMB share using OS.File.writeAtomic in a ChromeWorker

I’m writing to file using OS.File.writeAtomic from a ChromeWorker but that errors out with a “file not found” when I write to an smb path (\server\share\dir\file). In the main thread using nsIFileOutputStream I can write to the same path without problem. Is there anything I can do about this?