I recently extracted tor-browser-linux64-6.0a4_en-US.tar.xz on a mounted drive. And tried to start the browser.
The Browser didn't open due to not recognizing the .desktop file which starts the Browser. Later, I was advised to copy and paste it in home directory.
And after pasting it in home directory, it no more shows permission problem or recognizing problem regarding the .desktop file by bash but now, it is showing permission problem in execdesktop file in Browser directory of Tor Browser's root directory.
user@user's-desktop:~$ cd tor-browser_en-US user@user's-desktop:~/tor-browser_en-US$ ./start-tor-browser.desktop /usr/bin/env: ./Browser/execdesktop: Permission denied