You can install media download apps, I use Download Helper (Firefox) and Flash Video Downloader (Chrome). What I do is open the specific post at an individual tab - ex: http://darrencrissmusic.tumblr.com/post/49747580068/glee-cast-all-or-nothing - and then I press play and it will be available for download through the app.
I’m really bad at explaining but I hope I helped.
Glee Cast - We Will Rock You
Darren’s Version of Call Me Maybe at the GLAAD AWARDS
Note: I edited this with the better audio
Moondance - Darren Criss - PS Arts 2013 (mp3)
(audio courtesy of catastropheofmypersonality who was nice enough to let me post this)
Adele & Darren Criss - Skyfall & I Still Believe [Mashup]