I can pretty much guarantee you Feynman didn't either -- when he was actually working with relativistic equations. The idea of a rest mass makes everything way, way simpler.
There was a Feynman quote in one of my physics texts that left a big impression on me -- basically saying that you shouldn't call yourself a physicist until you can understand the same physics using multiple models, gleaning insight from whichever is the most useful in context.
>you shouldn't call yourself a physicist until you can understand the same physics using multiple models
This applies to pretty much any field. Feynman was a great physicist from this point of view.
There was a Feynman quote in one of my physics texts that left a big impression on me -- basically saying that you shouldn't call yourself a physicist until you can understand the same physics using multiple models, gleaning insight from whichever is the most useful in context.