TorBrowser 7.x Mac - Disable kMDItemWhereFroms extended attributes at least in Private Browsing Mode
In late 2016, Mozilla developers implemented kMDItemWhereFroms extended attribute metadata on macOS to behave more like Safari (however Safari, rather surprisingly for Apple, doesn't write xattrs in private browsing).
When files are downloaded, Firefox (v51+) writes the URL of downloaded files to a kMDItemWhereFroms entry in the file's extended attribute, even in Private Browsing mode. This metadata can be viewed using "xattr -l " and removed using "xattr -rc ", but on later versions of 10.12 this metadata is usually also written to ~Library/Preferences/com.apple.LaunchServices.QuarantineEventsV2
I plan to file a bug on bugzilla and ask the devs who implemented it whether they could add an about:config pref or disable the functionality in private browsing, but in case they don't respond, I thought I'd file a ticket here too since TorBrowser is now on v52ESR.
Here's the bugzilla bug where the developers originally implemented the kMDItemWhereFroms functionality.