Bitcoin, the flagship digital coin that spectacularly crashed in late 2017, has staged a comeback in recent months – tripling in value since the start of 2019 thanks in part to Facebook’s cryptocurrency plans. 

Bitcoin rose to fame when its value surged about 2,200% in a year before the bubble burst in December 2017, wiping out half of those gains in slightly over a month.

But the steady decline that followed – partly because of moves to regulate digital currencies and several high-profile hacks — was arrested in January...