It would most likely had been a segmentation fault, which is where some code didn't play nice with some other code. In this case, this would most likely had been the WebKit2 library. There was a bug in the past that caused exactly what you described, which has since been fixed.
Bad installation medium could also be a possible cause of faulty installations. You can verify your downloads to be absolutely sure.
For applications, try running them through the terminal. Some also accept a -v (verbose) parameter, so you can see more inner workings of what it's doing.
ubuntu-mate-welcome --boutique -v
(In future, Software Boutique will become its own program, but it's part of 
Welcome for now.
For general system and kernel (usually hardware related) logs, check the Log File Viewer and check out syslog, dmesg and kern.log, etc.