I had the same after forcing Firefox to do hardware acceleration on my Nvidia GPU. Firefox wanted to disable it, but I wanted to use my GPU anyway. Perhaps try

I had the same after forcing Firefox to do hardware acceleration on my Nvidia GPU. Firefox wanted to disable it, but I wanted to use my GPU anyway. Perhaps try resetting the GPU acceleration configuration? Firefox isn't as stable as I would like it to be, but it's much better than any Webkit alternative I can find on Linux.