On my iMAC running Mohave, JamKazam crashed every time on launch since the mid-April update. I tried starting in SAFE Mode, using app cleaner to completely remove and reinstall. I tried boot with another USER for the mac, I tried running disk first aid, I tried installing by both Firefox and Safari, I tried disabling the Firefox add-ins. None of this worked. When I re-read the CRASH Log created when JAMKAZAM crashes, I found what appeared to be the culprit, an internet plugin different from FB one mentioned above which was not on my system anyhow. Found this plugin and used app cleaner to delete it:
/Library/Internet Plug-Ins/npwViewer_turn.plugin/
It seems this was a plugin that was installed on the prior iMAC (prior to activating the 2012 iMAC in 4/2019). That plugin is used by my external Webcam in SAFARI to operate the Webcam. This plug-in was never explicitly installed after 2012 iMAC activation, but it remained on the hard drive when the contents of old iMac was transferred to newer iMac.
JAMKAZAM now works!!
/Library/Internet Plug-Ins/npwViewer_turn.plugin/
It seems this was a plugin that was installed on the prior iMAC (prior to activating the 2012 iMAC in 4/2019). That plugin is used by my external Webcam in SAFARI to operate the Webcam. This plug-in was never explicitly installed after 2012 iMAC activation, but it remained on the hard drive when the contents of old iMac was transferred to newer iMac.
JAMKAZAM now works!!