I have enabled adblock, media is disabled and flash and pictures too. But when commenting on youtube videos in projectmaker, it starts to get REALLY laggy after 15 minutes or so. Just try it out.
...just wanted to add, that in my previous version 5.9.8.1 it worked fine, no lag.
...and another thing... I just got a 'browser failure' message with a 'restart browser instance' button in PM, which I never ever got before.