What's going on
It is most likely due to JamKazam trying to load plugins from the folder on your system /Library/Internet Plugin-Ins (these are plugins that your normal browser uses, like Safari).
On my own machine, I had to move a plugin out of that directory in order to get JamKazam to load.
In the commands below, I move the any plugin starting with fbplugin* to my desktop ( that way I could move it back later, if I like). I believe this is the Facebook Photo Viewer plugin... so I should be able to get it back by going to Facebook.
Here are the steps to fix
Open Terminal (hit Command + Space, and type Terminal). Then paste this into terminal to move the troublesome plugins out of the way. You will be prompted to enter your login password because of the use of 'sudo'. You need elevated privileges to move these plugins out of this folder; that's why there is a password prompt.
sudo mv /Library/Internet\ Plug-Ins/fbplugin* ~/Desktop
sudo mv ~/Library/Internet\ Plug-Ins/fbplugin* ~/Desktop
We are working to get a real fix for this.