From the website:
We're Sorry
This site requires the use of Microsoft Internet Explorer Version 6 or Later
Why can't I use another browser?
This site has some cool features that simply do not work in other browsers. Since you probably have Internet Explorer on your system anyway, that means our fine products, great prices, and twenty-five plus years of experience are just a click away. Please take the extra step. You'll be glad you did.
Sorry, what "cool" features can your web developer not get to work in Firefox? Will these "cool" features help put your products in my hands? Will they make my online shopping any easier? Gee, what if a visitor to your website uses an Apple computer - do you prefer not to sell those folks??
Sorry, but as someone who dabbles in web design I find it extremely annoying in this day and age that this nonsense exists. It's like asking shoppers at a brick and mortar store to learn some stupid secret handshake before they can open your front door.
Have a look at
www.paintscratch.com for paint codes, custom filled spray cans of various sizes, painting materials for professional painting systems, etc. And they don't seem to care what browser you're using.