On my PC, when it happens, it not only freezes the selected tab but also one CPU core goes up to 100% load and stays there until I close that tab (non-multi-threaded) or Firefox (multi-threaded). Maybe some kind of endless loop or wrongly programmed recursion. Just guessing, I'm not a javascript programmer.
Unfortunately, my first approach was to blacklist https://www.geocaching.com/account/scripts/custom/message-center-header-widget.js with AdBlockPlus but this makes the whole website unusable. For example, on geocache pages, logs are not loaded any longer, and also the mini-map preview won't work, and coordinates cannot be changed any longer. In other words, not loading message-center-header-widget.js at all seems to break most (all?) other javascript code on that page.
Taking a photograph, really cool idea. Have to remember that! But I'm using your add-on now, so hopefully I won't have any more crashes. :-) Again, thank you so much!