Mozilla, Firefox - NPAPI (Extended Support Release) Update package index files (run sudo apt-get update ).
And just in case the adobe-flashplugin package is missing, you may not have the 'Canonical Parter' repo activated in Software & Updates / Software Sources, see Ubuntu's help page for 14.04 trusty or 16.04 xenial. Make sure you have the Universe repository enabled (in Software Sources, accessible from Software Center -> Edit -> Software Sources, or sudo add-apt-repository universe or see How do I enable the 'Universe' repository? ).ġa.