$ rpm -qf /usr/lib/browser-plugins-npapi/nsdejavu.so
mozilla-plugin-djvu-3.5.21-alt1
$ rpm -q seamonkey
seamonkey-1.1.16-alt1
$ 

seamonkey reports the following errors on some pages:

$ seamonkey http://picasaweb.google.com          
LoadPlugin: failed to initialize shared library /usr/lib/browser-plugins-npapi/nsdejavu.so [/usr/lib/browser-plugins-npapi/nsdejavu.so: undefined symbol: XtShellStrings]
LoadPlugin: failed to initialize shared library /usr/lib/browser-plugins-npapi/nsdejavu.so [/usr/lib/browser-plugins-npapi/nsdejavu.so: undefined symbol: XtShellStrings]
$ 

The first time I opened this page with seamonkey, there were even more error messages:

 LoadPlugin: failed to initialize shared library libXt.so [libXt.so: cannot open shared object file: No such file or directory]
LoadPlugin: failed to initialize shared library libXext.so [libXext.so: cannot open shared object file: No such file or directory]
LoadPlugin: failed to initialize shared library /usr/lib/browser-plugins-npapi/nsdejavu.so [/usr/lib/browser-plugins-npapi/nsdejavu.so: undefined symbol: XtShellStrings]
LoadPlugin: failed to initialize shared library /usr/lib/browser-plugins-npapi/nsdejavu.so [/usr/lib/browser-plugins-npapi/nsdejavu.so: undefined symbol: XtShellStrings]

If the reason is that my libX* are too old:

$ rpm -q libXt libXext
libXt-1.0.5-alt2
libXext-1.0.4-alt2
$ 

then this means that the plugin package or the seamonkey package shold have more strict dependencies on the version of libX*.