Firefox allows you to choose your search provider in a dropdown each time you search, so this is useful if you still want results from Google sometimes. Firefox also allows you to make a search provider the default.
To get Firefox to recognize Solve for All as a search provider, first go to the home page of Solve for All. After that, find the search box in Firefox, which looks like this:
Click the down arrow next the icon for your default search provider in your search box and choose Add "Solve for All":
After that the search box will show that Solve for All is the current search provider:
Then your queries in the search box will show results from Solve for All. Nice!
If you want to change search providers as you browse, just click the down arrow in the search box and choose the one you want to use. Very convenient, especially if you're not ready to give up Google totally.
You are done. Enjoy!