After 10 minutes of searching and toggling options, I still can't figure out how to disable "quickfind" (aka "highjacking the slash key") in Firefox. I really thought setting the "quickfind" option to false would do it, but apparently not :(
Finally found the setting in about:config. It's called "accessibility.typeaheadfind.manual" (which doesn't mention "quick find" and doesn't actually seem related to accessbilitiy to me). How did I find it? Had to track down the code change that resolved the bug I eventually found on this topic: https://hg.mozilla.org/mozilla-central/rev/c3559084af4a