Albert Barnes Commentary Psalms 78:21

"Therefore Jehovah heard, and was wroth; And a fire was kindled against Jacob, And anger also went up against Israel;" — Psalms 78:21 (ASV)

Therefore the Lord heard this, and was wroth - See Numbers 11:1, Numbers 11:10.

So a fire was kindled against Jacob ... - Fire may be used here, as in Numbers 11:1, as an emblem of wrath; a fire may have been literally sent down to consume them.