Try this: https://support.mozilla.org/en-US/kb/changes-affecting-adobe-flash-firefox-mac
The link says that it's only for mac, but I found forum posts here on kongregate saying that this fixed it for windows too.
Hello Rand8, we had some maintenance to perform on the server to make sure it's up and ready to take action. Now it's perfectly fine, feel free to hop on and beat up that raid boss!
Hey Rand8, wrote down your input to check. A few ideas in the meanwhile: 1/after an update, I heard from other players that were having issues on firefox that it helps if you clear cache and then refresh; 2/would you consider switching to Chrome? (the game works better on chrome). Please let me know if you managed to get into the game with any of these ideas. Best wishes, Leena
 "Christmas Idle Clicker"){kind=icon}
 "Space Idle Cliker"){kind=icon}
 "Block Invaders"){kind=icon}
 "Idle Creature Fight"){kind=icon}
 "Forest Clicker"){kind=icon}
 "Pixel Gold Clicker"){kind=icon}
 "Idle Portal Guardian"){kind=icon}
 "Idle Alien Click"){kind=icon}
 "Fisherman - Idle Fishing Clicker"){kind=icon}
 "Wizard (And Minion) Idle - Beta version"){kind=icon}
 "Swarm Simulator: Evolution"){kind=icon}
 "Colorius"){kind=icon}
 "Military Capitalist: Idle Clicker"){kind=icon}
 "Idle Space Tycoon"){kind=icon}
 "Ant Empire"){kind=icon}
 "Idle Chopper"){kind=icon}
 "Idle Tcc"){kind=icon}
 "The depths idle"){kind=icon}
Thanks, these are coming asap