This is a virus not Firefox I would recommend Malaware bytes install and run scan. [https://www.malwarebytes.org/antimalware/ Malwarebytes]

Although a few sites build that in, if it appears everywhere, the most likely culprit is an add-on. Here's my suggested procedure for tracking down and cleaning up bad add-ons and other ad injectors. I know it seems long, but it's really not that bad. (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 in smoking out 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) Open Firefox's '''Add-ons page''' using either: * Ctrl+Shift+a * "3-bar" menu button (or Tools menu) > Add-ons * in the Windows "Run" dialog, type or paste <br><code>firefox.exe "about:addons"</code> In the left column, click '''Plugins'''. Set nonessential and unrecognized plugins to "Never Activate". In the left column, click '''Extensions'''. Then, if in doubt, disable (or Remove, if possible) unrecognized and unwanted extensions. Often a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step. Any improvement? (3) You can search for remaining issues with 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. Success?