Tor Browser 8 can't install new addons

Tor Browser says “uBlock Origin could not be installed because Tor Browser cannot modify the needed file”.

The log says:

1533738639975 addons.xpi ERROR Failed to move file /home/amnesia/.tor-browser/profile.default/extensions/uBlock0raymondhill.net to /home/amnesia/.tor-browser/profile.default/extensions/trash: [Exception… “Component returned failure code: 0x80520015 (NS_ERROR_FILE_ACCESS_DENIED) [nsIFile.moveTo]” nsresult: “0x80520015 (NS_ERROR_FILE_ACCESS_DENIED)” location: “JS frame :: re//gre/modules/addons/XPIProvider.jsm :: _installFile :: line 582” data: no] Stack trace: _installFile()re[//gre/modules/addons/XPIProvider.jsm:582](//gre/modules/addons/XPIProvider.jsm:582) _installDirEntry()re//gre/modules/addons/XPIProvider.jsm:663@

Parent Task: #15023 (closed)

Original created by @segfault on 15773 (Redmine)