Hello, This sounds like a problem possibly caused by adware on your pc. Please go to firefox > addons > extensions & remove any suspicious entries (toolbars, things that you have not installed intentionally, don't know what purpose they serve, etc) and do a full scan of your system with the free version of [http://www.malwarebytes.org/ Malwarebytes] & [http://www.bleepingcomputer.com/download/adwcleaner/ adwcleaner] . [[Remove a toolbar that has taken over your Firefox search or home page]] [[Troubleshoot Firefox issues caused by malware]] In case this doesn't solve the issue please try this: go to firefox > help > troubleshooting information > profile folder - "show folder", then a new window will open up. in this window look out for a file named user.js (it might be used to overwrite your custom settings). in case it is present , delete or rename this file and restart firefox afterwards. [[How to fix preferences that won't save]] Please let me know if that doesn't help. ------------- Ref - phillipp in this support thread - https://support.mozilla.org/en-US/questions/949572