I'm seeing a brief hang of my browser (beachballing etc) under Firefox 34 on Mac OSX 10.9. CPU usage jumps to about 90% during this brief hang which lasts a second or three.
I can replicate the similar CPU usage with Opera 26.0, Yandex 14.12, SeaMonkey 2.31 and Sleipnir 4.5.1
I can’t replicate it in Safari 7.1.2
Only in Firefox do I actually experience a brief beachballing within Firefox.
This only seems to happen on significantly sized pages, I see it especially on TV story pages.