hello, maybe an addon or toolbar is inserting this code into websites - please try if sites load correctly in safemode & if so remove all extensions in firefox > addons > extensions, that you don't have installed intentionally or that might look suspicious (especially toolbars of all sorts). also have a look in the windows control panel / programs section and also uninstall toolbars etc. that are listed there... [[Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems]] [[Troubleshoot Firefox issues caused by malware]]

Found a couple of toolbars I didn't recognise in my Firefox add-ons and disabled them. Seems to have solved the problem. Many thnaks