For those who may not be aware, 'watch instantly' on Netflix does not work well in Firefox on the iMacs. This is an issue that can generate a lot of patron complaints so here's the 411:
Short version: If Netflix doesn't work on the Macs you have two options: Reboot and/or use Safari.
Long version:
Netflix uses MS Silverlight for it's DRM and it seems that when
parental controls are enabled on the macs (we use parental controls to
control patron access to applications) that Silverlight and Firefox do
not play well together. What usually happens is that when we are
creating a new master image for all the machines we make sure that all
the plugins are working but there are almost always issues with Firefox
and Silverlight that, sooner or later, requires a reboot. Add the fact
that after some random number of days/weeks later watching Netflix
becomes totally broken in Firefox. This is due to changes made by either Netflix or MS on the server end as nothing has been changed on the
machines. I am running some updates on a master image right now for the
media center and it looks like I can't get Netflix to work at all in the
latest version of Ffirefox. Point people to Safari if they wish to watch Netflix.