To change your default homepage in Firefox for Mac OS X, go to the Firefox menu and click on Preferences.
On the General tab in Preferences, delete the currently entered homepage, and replace it with the full address of the homepage of your choice.
If you want to remove the Ask New Tab page, please follow these instructions on how to remove the add-on from Firefox.
Next, if you want to change the default search engine for Firefox, you can access the option by clicking on the magnifying glass icon, found in the search box on the top-right corner of the browser. When you hover the cursor on top of the icon, you will see a triangle icon appear. Click on it to see the list of available search engines, which can be used for your next search. If you want to make a specific search engine the default, click on the last item: “Change Search Settings”. This will open Firefox Options to the appropriate section. Under “Default Search Engine, pick the search engine of your choice from the drop-down menu.