(I assume you mean the stand-alone programs on your computer, and not Office online, which may work differently in Firefox and Microsoft's own browsers.) Firefox should not interfere with starting and using Microsoft Office! Before diving in too deep, have you shut down Windows and started it up again since the problem began? Just in case some updates are not yet fully complete. What version of Office do you have? This article describes how to do a "repair" using the Office installer (but doesn't mention whether it works with Office 2016): https://kb.wisc.edu/helpdesk/page.php?id=9344 ---- Unfortunately, some websites that advertise Firefox downloads on search engines provide bundles with various unwanted programs that may have negative consequences for your system. Could you double-check for that problem as follows: (1) Open the Windows '''Control Panel''', Uninstall a Program. After the list loads, click the "Installed on" column heading to group the infections, I mean, additions, by date. This can help surface undisclosed bundle items that snuck in with some software you agreed to install. ''Be suspicious of everything you do not recognize/remember, as malware often uses important or innocent sounding names to discourage you from removing it.'' Take out as much trash as possible here. (2) Supplement your regular security software with some of the '''scanning/cleaning tools''' listed in our support article: [[Troubleshoot Firefox issues caused by malware]]. These on-demand scanners are free and take considerable time to run. If they finish quickly and especially if they require payment, you may have a serious infection. I suggest the specialized forums listed in the article in that case.