There are many people who browse the internet using Internet Explorer. There are also a great number who browse the internet using Mozilla Firefox. It is really a matter of personal preference. I use both browsers frequently. Most techies prefer Mozilla Firefox. As a programmer and web designer, I primarily use Mozilla Firefox when I surf the internet.
When I design and build websites, I test them in both browsers. I have come across some websites that work only in Internet Explorer. That basically means you will only sell to people who browse to your site using Internet Explorer.
So maybe you do not want the business of those who surf in Mozilla Firefox. I doubt it. If you are in business, you want to make sales, period. Not just to one crowd of browser users.
I've come across websites that could have been viewed in Mozilla Firefox, but you could not place an item in the shopping cart and purchase it. More lost sales.
I have also seen sites that display correctly in Mozilla Firefox and not in Internet Explorer, and vice versa. There are some little quirks and code issues that require some tweaking to display correctly in both browsers.
I do not try to test every site in every site browser that comes along. New browsers come along that are not fully tested and may or may not become a mainstay. The majority of surfers are using either Internet Explorer or Mozilla Firefox.
If you are a website owner, I recommend you download both browsers. Then test and view your website in both.
There are also some inconsistencies in some of the site builders when viewed in different browsers. I know of one in particular that in the admin panel of the builder in Internet Explorer, you have a choice of editing using WYSIWIG or HTML mode. However, in the same site builder admin in Firefox Mozilla, the WYSIWIG mode is inoperable, and you have to edit pages and content in plain HTML.
That is fine if you are proficient in HTML code. If not, you'd fare better loading the builder in Internet Explorer. The designers of the site builder obviously did not check their builder's compatibility in both browsers before release.
I once contacted two business owners to inform them that I use Mozilla Firefox as my browser and could not purchase items on, or view portions of, their websites. Both of them told me that they were aware of the issue. Several people had written them to let them know. They said, "We do not know how to fix it. Our site builder only allows checkout or site viewing in Internet Explorer."
If that were me, I'd be really concerned about the sales I was losing because of browser incompatibility. I would most likely change site builders. A lot of people are using both of these browsers. As a business owner, I want to make sales to all of them, not just shoppers of Internet Explorer or Firefox. I want the business of all of these surfers.
Make sure your site functions in the popular browsers. If not, you could be losing money.