Foo Fighters are working up to the release of a new album, and while they didn't leak anything of significance from their upcoming disc, they did break out a few tracks that aren't usually part of their set while playing their headlining set at the Firefly Festival in Dover, Delaware, over the weekend.

The group headlined the Friday (June 20) festivities, closing out the Firefly festival fun in front of 80,000 people. And while the performance did include many of the band's staples, such as 'This Is a Call,' 'Monkey Wrench' and 'Times Like These,' Dave Grohl and crew carved out part of their set for a trip down rock and roll's memory lane.

"I love rock and roll as much as the next guy, maybe even f---ing more than the next guy. I love being in the Foo Fighters," stated Grohl. "But tonight, for the next four or five songs, we're a f---ing bar band called The Holy S--ts that plays f---ing classic rock songs, what about that s--t?" And with that, Grohl launched into the opening guitar licks of the Alice Cooper classic, 'School's Out.' Video of the performance can be seen above.

The classic rock covers kept coming with the band riding the groove of Rolling Stones' 'Miss You' (seen below), while Grohl added a little bit of Mick Jagger swagger to the vocals and keyboardist Rami Jaffe got a mid-song breakdown. Next up came a rendition of Van Halen's 'Ain't Talkin' 'Bout Love,' which Grohl dedicated to drummer Taylor Hawkins (seen below). The drummer took lead vocals on the track, while the band provided support.

Finishing out the classic rock portion of the set, Foo Fighters trotted out the Queen and David Bowie favorite, 'Under Pressure.' Both Grohl and Hawkins handled vocals on the track with Hawkins taking on some of Freddie Mercury's high parts. Fan shot footage of the performance can be seen below.

The show was also notable for the fact that guitarist Chris Shiflett played the entire set in a chair. Grohl explained his guitarist's condition, telling the audience, "Chris broke his foot or his ankle or something, but he came out here to play for you guys anyway. You know how you did it? By being f---ing old."

Look for Foo Fighters starting to book more dates for the fall, as their new album is due in November, the same month that their 'Sonic Highways' documentary debuts on HBO.

Watch Foo Fighters Perform Van Halen's 'Ain't Talkin' About Love'

Watch Foo Fighters Perform The Rolling Stones' 'Miss You'

Watch Foo Fighters Perform Queen + David Bowie's 'Under Pressure'