As of 2015-05, the old "pepperflashplugin-nonfree" is deprecated in favor of an official, maintained, one-step package called adobe-flashplugin, which works for Firefox and Chromium and derivatives, but not for Yandex.Browser 46.0.2490.3623 beta (64-bit version) on November 2015. No terminals, no multiverse.
Add the Canonical Partners software source, and install adobe-flashplugin. See Chromium/Getting-Partner-Flash.