I have spent a few days trying to fathom out why Opera Dev doesn't load Flash.
Despite copying the latest libpepflashplayer.so (plus manifest) to various locations specified in pepper_flash_config.json (below) as well as ~/.local/opera/plugins and ~/.mozilla/plugins etc it just doesn't load. Firing up Opera Stable 42.0.2393.94 on the same machine and it all works fine although Opera reports the version as 99.999.999.999:
Adobe Flash Player
Shockwave Flash 99.999 r999
Type: PPAPI (out-of-process)
The Adobe Flash page (http://www.adobe.com/uk/software/flash/about/) reports it as being the latest:
"You have version 24,0,0,186 installed"
It has all been working fine in Opera Developer for the last year so not sure what has changed.
"PepperFlashPaths" : [
Version: 43.0.2431.0 - Opera is up to date
Update stream: developer
System: Ubuntu 16.04.1 LTS (x86_64; LXDE)
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2914.3 Safari/537.36 OPR/43.0.2431.0 (Edition developer)