I'm putting this forward not only from my experience but also two of my friends who have had similar problems. This is a problem that has happened many times in the last couple of days, I belive the cause is an errorsafe advertisement on MT that's hijacking the browser. I just want to check that it's universal as so far I can only tell that it's me and my friends.
Basically one of those pop-ups appears on the screen saying theres such and such an error, normally these are fine and can just be closed of cancelled however this one is different. When you click close or cancel the ad will shrink then re-open an errorsafe page in the same window, rather than opening a new one and many a time have I ended up closing the ad window, which was my MT window. It really is becoming a pain as it's happening again and again.
I'll add that I've noticed this on IE on other computers but I can't remember if it was happening on my firefox at home, I'll update this post soon as to whether it is or not. Basically just want to check how many people this is happening to and then if it isn't just me, request that something be done. The page I've taken notice of is for errorsafe however there may have been more than one and again I will take more notice in the coming days.
EDIT: To make solving the problem a little easier if you are encountering the problem can you also indicate what browser you are using.
EDIT 2: Well I've found that good old firefox is actively blocking the errorsafe pop-up hijack ad, which I think proves that it definately must be there for everyone (and of course that firefox is superior!)