I've had a few questions about interface, but for the most part it's intuitive and I've had very few questions even from older people. Not hearing anything is a good sign.
I've had none of the UI issues you have (Firefox, Safari) and have heard none from any user. Weird!
Did they do an overhaul recently? Maybe people are remembering an older version.
I had to use LastPass at work, maybe 2 years ago, and I can confirm, it may have had the worst user interface (both in terms of aesthetics and usability) of any webpage I've ever had to use. I simply couldn't believe any self-respecting developer shipped that.
I've had none of the UI issues you have (Firefox, Safari) and have heard none from any user. Weird!