Here is more detail about creating custom keyword searches. For example, I have a Bugzilla keyword search so the keyword "bug" will expand the URL "https://bugzilla.mozilla.org/show_bug.cgi?id=%s". Thus, entering "bug 1000000" in the address bar will expand to "https://bugzilla.mozilla.org/show_bug.cgi?id=1000000".

https://support.mozilla.org/en-US/kb/how-search-from-address...