Ok my experience with firefox not loading so far has kinda revolved around upgrading xulrunner to version 22.214.171.124-1. I think it's an upgrade from the pclos big update, but either way as soon as I upgraded it, I could no longer get firefox to load. So I downgraded xulrunner to 126.96.36.199-1 & now I can get firefox up and running again.
You can try downgrading these packages by using the force option in synaptic.
You click on package in the toolbar of synaptic, and then select force version. Then from the pop up window, select the 188.8.131.52 version. You'll want to have the package highlighted that you want to force a version for.
Also you'll have to do the same for all three xulrunner packages
Also for those of you that are not comfortable forcing the version, or cannot force the version for whatever reason. Then I put together the xulrunner rpms for version 184.108.40.206 and you could wait for Anurag to put them into the repo, and then go ahead and install them.