Does your forum look the same on all browsers? For instance, have you checked your forum's appearance on all browsers such as Firefox, Opera, Chrome and Internet Explorer? And, is your forum optimized for all?
I never really understand the difference of browsers and how it affects the forum appearance, haha. I never bothered to check it; after all members will use different browsers and they will come to us if they find something strange when browsing the forum. I do think it's important to optimize the website for all browsers, though. Even mobile version, as it's getting popular now.
I try to view my projects on whatever devices or browsers I can and then leave the rest up to my members to report. I typically trust that the designers have tested this before selling the theme.