Came a cross an interesting issue in that when browsing to the Lync Dial web page we were getting the certificate was not trusted. This did not occur with Internet explorer.
Naturally, I opened up the MMC console and added the certificate snap in to confirm that the Root CA for the Domain joined computer was installed in the trusted Root Certificate store.
Because Firefox was complaining about the Intermediate Certificate not being trusted I checked to see if Firefox is reading it from the Computers Cert store or it's own. It appears Firefox builds it's own Trust list and was not reading the RootCA from the Trusted Root Certificate Store. Notice no SeaRoot Cert.
So I exported the Certificate from the local Machines Root Certificate Store and imported it into Firefox
Now we can see the Root CA and Firefox opens up the Dialin Webpage with out a certificate warning or prompt just like IE.