See:

• https://malwaretips.com/blogs/?s=offers4U

hello,,my laptop is Mac air....how to deal with this thx

Did you read the article?

• https://malwaretips.com/blogs/remove-offers4u-mac-os-x/

See also:

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

You can check for recently installed suspicious or unknown extensions.

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

You can open the about:config page via the location/address bar and search for prefs that refer to offers4U. You can reset user set (bold) offers4U pref(s) on the about:config page via the right-click context menu to the default value. If you still have problems with preferences, see:

• http://kb.mozillazine.org/Preferences_not_saved

Thank you for your reply but I tried it doesn't work unfortunately.....so sad........any ideas? thanks a lot!

I'm not on Mac, so if you can't solve it with the instructions in the article then best is to ask advice at a forum that deals with malware removal.

• https://support.mozilla.org/kb/troubleshoot-firefox-issues-caused-malware