A Problem with Timing

I have recently created a movie of my 2 1/2 year-old daughter reading her favorite book. The movie simply consists of each page of her book with a voice over (mp3) for each new page. All mp3s are on a separate layer of the timeline and are attached to a corresponding frame on that timeline. As she reads each word on a given page, the word is underlined to keep up with her reading (also on a separate layer of the timeline). My problem is that the timing of the underlined words with the corresponding mp3 file is perfect when I view the swf on my desktop, but when I publish it to an html file and view it in a browser, the underlined words lag in relation to the sound. Is there a known issue here that I can fix? Something I need to do with my publish settings maybe?

Thank you for your assistance.