All biggies use FLOSS nobody gives back.

Take all the big companies in the IT world. They have used FLOSS in one way or the other. But when it comes to giving back to the same FLOSS projects they act smart. They take out all the loop holes in the FLOSS licensing and use it to shield their proprietary ways. They always resist using software licensed in gpl v3 which is one of the best FLOSS license I have come across to preserve the FLOSS ecosystem. The main reason a FLOSS developer goes for a lesser restrictive license like gpl v2 or bsd/apache license is that proprietary biggies love those licenses and the possibility of its use and reach to users increase. If a developer is interested in vast reach then he would never release it with gpl v3.

The linux kernel is the best example for software licensed with gpl v2. If it was licensed with gpl v3, I dont think google would have put that kernel in android systems. They in turn would have gone for a bsd kernel. Which is the same case with apple. Though linux is far ahead in terms of hardware support compared to bsd kernel, for apple it worked nicely since they are not here to support all the hardware in the world. But for android, it was different. They wanted to support anything and everything on the planet so google went ahead with linux gpl v2. Given the same hardware support or if linux is licensed in gpl v3, I am pretty confident that google will go with bsd kernel. They just have to re-write their virtual machine, and all the apps would run fine.

facebook also uses lot of FLOSS software, but I have not heard about any code being given back to the FLOSS eco-system

The summary is, all these proceeding will stifle further innovations in the FLOSS world and there would not be any special FLOSS project which the biggies can parasite on. I appeal to all the biggies to come out with their usage of FLOSS projects and put the changes and improvements they have done back to the FLOSS ecosystem.