Persistent title popup in Firefox 3.0.4

Hi, can't find any other reference to this anywhere but I'm having a problem with the last title popup on a page appearing when my cursor is hovered over anything on a page. If an item has a title attribute the title changes but then it persists until the cursor passes over another item with a title attribute and so on. This seems to have been introduced with 3.0.4 but I'm not sure if it's a Firefox or Portable Apps problem as I only run Portable Firefox under Windows on my office laptop. Any ideas?