The second Alpha release in the new Firefox 28.x branch has been made available for download by Mozilla for all platforms, including Linux.
You should be used to it by now, but Mozilla doesn't provide any official information about the newly released Alpha versions, at least not immediately.
As always, the binaries for Mozilla Firefox 28 Alpha 2 can be downloaded and run without having to install anything, but you will have to be very careful because it will use any available Firefox profile, and some add-ons will not be compatible.
Remember that this is a development version and it should NOT be installed on production machines. It is intended for testing purposes only.