As advised by :
http://apple.stackexchange.com/questions/169948/updating-to-os-x-10-10-2-broke-q uick-look-previews-for-html-files/174079#174079
I've been doing a bit of tinkering with the qlmanage command in the Terminal.
It seems the -t option on an html file seems to work fine - it displays a small thumbnail of the file just fine. It's when I use the -p option to compute a preview of the HTML file that it fails on.
IE
qlmanage -t <path_to_HMTL_file> <-------------- thumbnail comes up fine
qlmanage -p <path_to_HMTL_file> <---------------- nothing
But
qlmanage -p <path_to_JPG_file> <-------------- thumbnail comes up fine
qlmanage -p <path_to_JPG_file> <------------------- preview comes up fine
Now comparing the outputs of both the HTML file and the control sample JPG file it would appear that the Web preview generator is crashing when it comes to HTML files. If you wait when you use the -p option on the qlmanage command to an HTML file it eventually produces what looks like the backtrace to a crashing thread. It then just hangs there doing nothing and you have to Control - C the qlmanage command to get out of it. When its working fine it just runs qlmanage as a program and displays the quicklook preview as a window you just quit out of.
Here's that backtrace :
http://pastebin.com/Gi0j4ZFh
Just wondering .... has anyone done the testing I've done and submitted that in their bug report ? Might be information they may want to add onto Bug # 19639311