Just adding that I had the same problem with Iron Portable 23, and am having the same problem with the latest release which I have just installed: Iron Portable 24.0.1350.0 (176001).
My OS is Windows 7 Professional, 64-bit.
The problem happens with a completely fresh install of Iron Portable as downloaded from this site, so it cannot be related to the profile, unless there is something wrong with the blank profile provided. (It also does not work if I import a profile from Iron Portable 23.)
Simple test: Go to http://xkcd.com
- a webcomic well known for having a second joke in its comic image title attribute. Hovering over the comic in the current release of Iron Portable does not show this.
Trying the same in the latest release of Firefox reveals the extra information.
If I was to attempt to fix this myself, I would begin by looking for any handling for title attributes in HTML tags. This may not be as easy as I make that sound(!) but that is where I would start.