Although I am using Arch Linux and not CentOS, in case it helps, I encountered a similar issue with a recent upgrade of firefox (to 33.0.2). The problem looked like a simple case of dependencies that somehow did not get handled properly by the package manager.
The initial problem I encountered when I updated firefox and tried to start it was
XPCOMGlueLoad error for file /usr/lib/firefox/libxul.so:
libicui18n.so.54: cannot open shared object file: No such file or directory
Couldn't load XPCOM.
I tracked down that libicui18n.so.54 is in the icu
(International Components for Unicode library) package, so I updated that package. I then tried to start firefox
and got
XPCOMGlueLoad error for file /usr/lib/firefox/libxul.so:
/usr/lib/libnss3.so: version `NSS_3.16.2' not found (required by /usr/lib/firefox/libxul.so)
Couldn't load XPCOM.
So, I tracked down that libnss3.so is in the nss
(Mozilla Network Security Services) package, so I updated that package too.
Then everything worked.
yum provides libvpx
??