Firefox's "open download folder" button opens sandboxed Downloads folder, not actual Downloads folder

[e-t-l]

After downloading a file in Firefox, I get the sbie Immediate Recovery prompt and accept it, moving the downloaded file into the host folder "C:\Users\etl\Downloads". Firefox, like most browsers, has an option in the Downloads panel to "open containing folder" of the downloaded item. When I press this button, it opens File Explorer at "C:\Sandbox\etl\FireBox\user\current\Downloads", which is the sandboxed version of the Downloads folder. Because the file has already been recovered to the host file system, it is not there.

What I don't understand is, why does Firefox launch File Explorer at the sandboxed directory, not the real one? In Firefox's about:config, the pref download.browser.lastDir = C:\Users\etl\Downloads\Installers, which means Firefox thinks it's downloading to the real host directory. So, shouldn't clicking the button launch that folder? (explorer.exe is a BreakoutFolder, by the way)