hello, it appears as if you have a user.js file present in your profile folder which may be used to overwrite your custom settings. 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 - in case it is present , delete or rename this file and restart firefox afterwards. afterwards your settings should 'stick'...

How to fix preferences that won't save

finally install the search reset addon - it will revert the most common customizations done by adware back to the default: https://addons.mozilla.org/firefox/addon/searchreset/

Great - thank you! That was driving me crazy! I was able to get it fixed in Safari but Firefox wasn't changing.

Thanks!!