Pre-5.0, if you had a Rip on your target in the execute phase and then used FB, any damage buffs you had when you used FB would in turn apply to the refreshed Rip. For example, if you had Tiger's Fury up when you used FB, the Tiger's Fury damage buff would be applied to the refreshed Rip on the target. Same goes for trinket procs, pots, etc.
Post-5.0, any damage buffs/procs/pots/etc that are active when you use FB in the execute phase will NOT buff the extended Rip. However, if you directly apply Rip with Tiger's Fury and/or pots/procs/etc and extend that Rip with FB, Rip will be extended with the same power as when you originally applied Rip. Simply put, FB extends the current Rip instead of refreshing it with a new Rip.
While this may not be that big of a deal at this stage, when you have access to the level 90 talents (specifically Dream of Cenarius or Nature's Vigil), knowing how Rip acts in the execute phase with respect to FB makes a big deal.