In the properties window, you can't currently press the save button until a file has been downloaded completely. Having to sit and wait several minutes just for it to complete feels very inconvenient. Couldn't it be possible to request the file to be saved even though it is still being downloaded?
There must be a tempfile already used for disk cache, so the only difference would be to add an event that if and when the download is complete, would move the tempfile to the target that was previously specified in the file chooser.
If possible, it could be logical if a download that is saved would appear in the browser's native download dialog, so that the saving (but not the download) could be canceled or even duplicated into further targets.