For me, this addon does not work when trying to assign either tilde or alt+` for tab navigation. The old swifttabs worked perfectly, but that developer abandoned it; now searching for a replacement, but this doesn't work in Firefox quantum versions. This appears to be because certain pages override the key bindings, so sometimes it will work to switch between tabs with the reassigned shortcut, but sometimes it will get stuck on a particular page. This is not acceptable, and probably a Mozilla issue more than the addon dev's issue.