That's good you have Roll20 working with Chrome. The problem in Firefox could be your ad-blocker, or any extension/add-on to the browser, or it could be something else. Best way to check and know is follow the Solving Technical Issues guidelines from Roll20's wiki documentation (link below), and that would involve testing your Firefox without the ad-blocker turned off. I'm sorry you're having trouble with the site. Can you please follow Steps 1-3 of our Solving Technical Issues wiki page, taking special care to temporarily disable all browser add-ons and extensions, temporarily pause your anti-virus, and try switching browsers (for Chrome/Firefox specific issues) to see if one of those components is causing the problem. If all of that fails, please follow Step 4 , including providing all of the necessary information, so that we can further assist you.