There are plenty openings you could use in blitz, but, i think the slow solid and positional openings need more thinking, thus you could lose. I would suggest playing like Mikhail Tal, make sacrifices without calculating the move too much, and try to complicate the position for your opponent. I have used this in many of my games,i complicate the position, Make a complex but possibly unsound sacrifice which confuses the opponent and the opponent might choose the wrong variation and lose trying to play fast, or, might think long, get the perfect move but finally lose on time. so the clock is also a thing you will need to think about in blitz.If you want me to suggest openings, then From white the kingspawn,Maybe kings gambit, the open sicilian which is my favorite,scandinavian and such.French is a solid opening from black and either play advance and lose time for your opponent or play the exchange variation. With the black pieces, against 1.c4 Nf6 i think is the best way to respond and after that try to enter the indian system, Nimzo or kings indian. For d4 i would say Nf6 isnt bad but it involves more thinking,so i like to play the dutch defence, leningrad variation which is not very popular a chess opening.iwold definately suggest sicilian defence Najdorf variation in blitz, though it seems very impractial because ofthe sharp lines and tactical,calculative pplay, as mentioned before you can confuse your opponent into time pressure, and of course though i recomend to do unsound sacrifices maybe, but this should be used very rarely and in very important positions. Remember, even if your playing online you are psychologically twisting your opponent into a very uneasy place.

There are plenty of openings you could use in blitz, but I think the slow solid and positional openings need more thinking, thus you could lose. I would suggest playing like Mikhail Tal. That is, make sacrifices without calculating the move too much, and try to complicate the position for your opponent. 

I have used this in many of my games. Complicating the position by making a complex, unsound sacrifice may confuse the opponent and make them lose on time or make a wrong move. Remember, clock is also a thing you will need to think about in blitz.

I'd suggest playing the king's pawn opening as White. Maybe the king's gambit, the open Sicilian, which is my favourite, Scandinavian, and such. French is a solid opening from black and either play advance and lose time for your opponent or play the exchange variation. 

With the black pieces, against 1.c4 Nf6 is the best way to respond. After that try to enter the Indian system, Nimzo, or King's Indian Defense. 

For d4, I would say Nf6 isn't bad but it involves more thinking, so I like to play the Dutch defence, the Leningrad variation (which is not a very popular a chess opening).

I would definitely suggest the Najdorf variation in Sicilian, though it seems very impractical because of the sharp lines and tactical, calculative play, as mentioned before you can confuse your opponent into time pressure. Of course, I recommend making unsound sacrifices wisely, when absolutely necessary. Remember, even if your playing online you are psychologically twisting your opponent into a very uneasy place.