get rid of yahoo search engine

1. Disable all Extensions and test.

Safari > Preferences > Extensions

To uninstall the extension, select it and click the “Uninstall” button.

2. Safari > Preferences > Search > Search Engine :

Select your preferred search engine.

3. Safari > Preferences > General > Homepage:

Set your Homepage.

4. Use free Malwarebytes Anti-Malware for Mac/ AdwareMedic to remove adware

https://www.malwarebytes.org/antimalware/mac/

Download, install , open, and run it by clicking “Scan for Adware” button to remove adware.

Once done, quit Malwarebytes Anti-Malware.

or

Remove the adware manually by following the “HowTo” from Apple.

http://support.apple.com/en-us/HT203987

5. Hold the shift key down and launch Safari

as per your inquiry regarding finding com.apple.safari.plist -- go to user library : click on finder > go > keep on holding option key > library > preferences > com.apple.safari.plist

secondly : in yosemite & older macs enter in safari preferences by using keyboard shortcut : command + comma and disable the extensions but in EL - capitan apple has permanently set extensions to off .

generally if issues are still there by using the method how to set home page i am not stating the method as other person has already posted , in this scenario if home page setting is problematic we do a basic troubleshooting steps .

1 . in user library > safari > remove topsites.plist restart from apple then empty the trash .

2. if it didn't helped : in user library: preferences > remove com.apple.safari.plist to trash also contents of folder caches , cookies , saved application state

in the rarest case , if major issues are in safari , we remove entire contents of it .

finally the last option left is restart from apple logo & empty the trash .

also sometimes if malware is there in the system it stops the user to set the homepage . i have already given manual method in my previous post how to remove malware from system library , user library .

also if the users views malicious websites that are having embedded contents unknowingly malwares or ad injection softwares are downloaded . to avoid it google has formed a diagnostic tool to find if a website is legitimate . http : //google.com/safebrowsing/diagnostic?site=

so how to use it : enter the above link in the top URL bar and select your desired link of that website , copy paste next to this link - then hit enter key .

google will immediately show how many to trojans are there in that website , at what date google searched the site .

if the site is suspicious or having trojans don't view it .

or directly open google safe browsing diagnostic tool .