It looks to me like it's somehow related to NFSv4, as the
/var/log/messages files on the affected clients contain repeated lines like:
nfsidmap[7508]: Failed to add child keyring: Operation not permitted
along with call traces from the hung firefox processes
kernel: Call Trace:
kernel: [] ?
Looks like its not the firefox update at fault but the new kernel, which was
also released about the same time, not playing nicely with our NFS file
servers. Hopefully this can be resolved soon, currently am having users boot
into the previous kernel version (2.6.32-573.26.1.el6.x86_64 as
