User-Agent:       Mozilla/5.0 (X11; Linux x86_64; rv:50.0) Gecko/20100101
Firefox/50.0
Build Identifier: 

Evince browser plugin hangs Firefox when displaying embedded PDF

Reproducible: Always

Steps to Reproduce:
1. When I uninstall --type application Evince and go to a website with an
embedded PDF (e.g.: office 365 email attachment and click on 'view') the frame
says 'you need a plugin to view this'. 
2. I install the --type application Evince (which includes the plugin for
firefox) and repeat
Actual Results:  
the browser just hangs.
I shade the window, and unshade it, and then it becomes completely grey. I must
either 'Terminate' the application or find the pid and kill it.

Expected Results:  
display the embedded PDF

I am in a KDE environment. Using stock Evince, and firefox:
MozillaFirefox-50.0-1.1.x86_64
evince-3.22.1-1.1.x86_64

32-bit Adobe reader plugin (version 9) works just fine.