In this tab, expand the options in Firefox’s search box, and select “Add Find man pages”:
Then expand the search box again, and select “Manage Search Engines...”
Select “Mankier", click the “Edit Keyword” button:
Set the keyword to “man”:
That’s it! Now you can type “man ...” in your address bar to go straight to the corresponding man page.
For example, type “man ssh” and hit return:
You’ll go straight to the ssh(1) man page: