Do you mean that instead of your preferred search engine, something called Safe Search has taken over?

Often this problem is caused and perpetuated by an add-on. The first step is to check for and remove any unknown/suspicious/troublesome add-ons. Here's my suggested procedure for tracking down and cleaning up bad add-ons, hijackers, and ad injectors. I know it seems long, but it's 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
  firefox.exe "about:addons"

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. Bear in mind that all extensions are optional, none come with Firefox, and you can learn more about them by checking their reviews on the Add-ons site.

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.

Can you regain control of your preferred search engine and start page? These articles have the steps:

• Change your default search settings in Firefox
• Startup, home page, tabs, and download settings

(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?

I suspect you are looking for a setting that is in your Search Engine such as Google; not in Firefox.

For the Google website you can set preferences on the Google results page via the gear icon in the top right corner, click that button to open the menu list and select Search settings.

• http://www.google.com/preferences?hl=en

Google settings are stored in a PREF cookie on your computer, so you need to create an allow exception to keep cookies for Google to save the settings, otherwise you have to repeat it.

For YouTube, see: Disable or enable Restricted Mode - YouTube Help: https://support.google.com/youtube/answer/174084?hl=en