Can you please clarify what you are seeing? Are you using a Google website in Firefox? If that is the case then it is very common of Google to target Firefox users with ads for Chrome

FireFox is not even open. Chrome is open (several tabs) but then all by itself, FireFox opens to an add to download Chrome for desktop.

Please follow, you may have to look up the programs to get new links. https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware and https://www.malwarebytes.com/adwcleaner/ and https://forums.malwarebytes.com/topic/9573-im-infected-what-do-i-do-now/ Post in only 1 forum and wait. Save the Reports. Do not delete anything, should ask for help especially when deleting from the registry

Note : Firefox 56.0.2 is current release https://www.mozilla.org/firefox/all/ Full Version Installer Note : Firefox 57 Quantum release date Nov 14th https://www.mozilla.org/en-US/firefox/quantum/ Note : Legacy Extensions will be disabled and or removed.

Please let us know if this solved your issue or if need further assistance.