I want to stop use of FireFox's built in HTML source viewer and use an external viewer. Tools|Options provides no way to do this. Poking around in about:config doesn't reveal anything either.

Surely this question has been asked and answered a million times already, but when I try to search for it on the Mozilla support web page I get millions of garbage hits about PDF files - and I can't find a way to get to an advanced search that excludes the term "PDF". Even the obvious guess of putting "-pdf" in the search field doesn't work. Even more mind boggling: searching for "advanced search mozilla support" turns up only garbage - nothing about how to do an advanced search.