Hey there rchrd-caldwell Welcome to the Firefox support forums. WebBrowser.exe is dware program, that displays pop-up ads and advertisements on web pages that you visit. These advertisements will be shown as boxes containing various coupons that are available, as underlined keywords, pop-up ads or advertising banners. If you believe you are experiencing any of these issues then the linkelyhood is that Malwarebytes is correct. There are a lot of support websites out there that will tell you how to get rid of these programs. I will list two of them below that I got from a quick google search. https://support.norton.com/sp/en/uk/home/current/solutions/kb20100811171926EN_EndUserProfile_en_us https://malwaretips.com/blogs/remove-webbrowser-exe-virus/ Best of luck. My antivirus is Webroot Secure Anywhere which runs alongside Malwarebytes which seems to work well. Best of luck, get back to us if you need anything else. Bradforth