same thing happen to me. i am using debian sid. before i do dist-upgrade a week ago. i have the same problem. FF use 97% of the CPU after i open few tabs (my laptop using 256MB + Via C3 1G CPU).. especially when i watch youtube.
i have to kill the process manually from the terminal because FF stop responding and the computer soooo slow. after upgrade FF use 15% of CPU. i don't think the problem solved yet. but i will know .. :P
