Click the Apple at the top left corner and open System Preferences by clicking it on the drop down menu.
When System Preferences opens click the "General" icon to open general preferences.
Scroll down to "Default web browser" Click the blue up/down arrows to the right of the current default browser.
Select the desired default browser from the drop down selection.
Close System Preferences and open a finder window to a directory that contains an html/htm file for Step 4.
Select any html/htm file in the finder window. ⌘+i is the keyboard shortcut to Step 4a.
Right click on any html/htm file and select "Get Info" from the pop-up menu.
Click the blue up/down arrows to the right of the current default browser for opening the browser selections available.
Select the default browser at the top of the list which you previously changed in System Preferences.
Click "Change All..." and then click "Continue" in the pop-up.
Double click any html/htm file found in a finder window to confirm it open in the desired browser.