[CentOS] Firefox and CPU spikes?

Is it just me, or does anyone else experience their CPU utilization 
spiking to 100% for about 5 to 10 seconds when Firefox is about to 
download a file, via http or ftp?   Then, after the file starts to 
download, the CPU usage drops back down to normal.

I've got Firefox 2.0.0.4 running on CentOS 4.4 32-bit.

Thanks.

Scott