Just to be clear, Mozilla has always signed beta builds, which were never a problem as far as I recall (I do a lot of outreach for Mozilla). We did get false positive complaints from nightly users who also used Symantec software, and we now sign nightlies, in part because of the reputation cred given to valid, signed binaries.
All releases and betas are signed with the Mozilla Corp. cert, there's a separate cert for nightly and Aurora builds, and a third cert for dev builds. I agree that we did have false positives with nightlies in the past, but I don't think that's happened for a while. If I'm mistaken, it'd be great to hear about them (I'll ping my contacts there, as well).
All releases and betas are signed with the Mozilla Corp. cert, there's a separate cert for nightly and Aurora builds, and a third cert for dev builds. I agree that we did have false positives with nightlies in the past, but I don't think that's happened for a while. If I'm mistaken, it'd be great to hear about them (I'll ping my contacts there, as well).