I have noticed something of a distracting idiosyncrasy in your performances. It has to do with your lip-synching, and I think we should come to an early agreement that lip-synching is clearly a feature of all your performances, be they "live" (in front of a live audience, anyway), or on video.
The sound "ell" /l/ is not made by touching the tip of your tongue to the exterior of your upper lip.
I suspect (or hope) that this is a piece of misinformation you were directly or indirectly given early in your professional career. Maybe someone told you to exaggerate everything you do in real life by 20 per cent when you're in the spotlight, and it made sense to you to move your tongue from behind your teeth to outside your mouth.
It's clearly seen here, in your first video:
This continues well into your career:
You know, though, having a sort of Spears video retrospective while choosing the right illustrative evidence, your songs are tasty little nuggets of pop from my youth. Sure, it's not very nourishing. Your music is the Toaster Strudel to say, Dave Matthews Band's egg white omlette, but it sure does hit the spot from time to time.
General Comment not directed to Britney Spears: Toxic is an effing awesome video. It's super fun, colourful, high-concept, and it's a catchy song. I love the campiness of the flight attendants. I don't like the metal triangle covering Britney's business. It doesn't match the spangles and I suspect it would cut.