Was looking at a webpage that had a "topic index" in a narrow frame along the left edge. The webpage author had specified that as the cursor passed over each topic title, the text rendition of that title would be switched to display as bold.
One multi-word title extended up to the right side of its enclosing column. When I put my cursor on the right end of the normal text for that title, that title got switched from normal into bold text. But the bold text happened not to fit within the column boundaries, so mozilla re-formatted that title into two lines (of bold text). Now that the page appearance had changed, the spot where my cursor still stood was blank underneath -- causing the topic title to be switched back from bold to normal text. And since normal text *did* fit within the column boundaries, mozilla re-formatted that title into one line (of normal text). But that again put text under where my cursor stood, causing the title to be switched from normal ... mikus (flutter flutter flutter ...)
