2.2.50 [CSS-Level2-2009] Section 16.2, Alignment: the 'text-align' property
The specification states:
Conforming user agents may interpret the value 'justify' as 'left' or 'right', depending on whether the element's default writing direction is left-to-right or right-to-left, respectively.
All Document Modes (All Versions)
justify value is interpreted as justified so that text is spaced out on all lines except the last line.