Silverlight Plugin Upgrade not reflecting dynamically on safari and firefox browser in Mac

Silverlight Plugin Upgrade not reflecting dynamically on safari and
firefox browser in Mac

I have web site which is built using silverlight.I am updating silverlight
from 5.1.20125.0 to 5.1.20513.0 on Mac system.I am downloading the dmg
file and installing it.I am polling for 2sec and checking the updated
version and than guiding the page to next.
I am repeatedly doing navigator.plugins.refresh = true; during polling.I
am not getting Updated silverlight version on the fly.
I found that,In safari(Mac) If i click to Help->Installed plugins.It
refreshes the plugin version immediatly and is visible as well and same is
true for firfox as well.
If I refreshes(Ctrl+R) the browser it is working fine and am able to
navigate to next page.
Please help me on this.