Key-kill-mode does not work on gecko >= 25 (it will cause Conkeror to not respond to key presses) but still works on Pale Moon (which is a fork of Gecko 24 despite having a 25.x version number).
Key-kill-mode is a generic page-mode for blocking keyup and keydown events, for example on websites that bind keys normally used by Conkeror. To use it, load the module, and then add tests so that it will be enabled on your problem sites. For example:
require("key-kill"); key_kill_mode.test.push(build_url_regexp($domain = "github")); key_kill_mode.test.push(/\/\/.*slashdot\.org\//);