Quit Firefox, vi into pentadactyl.xpi in your profile, edit install.rdf inside the xpi file (it's just a ZIP file) and modify the max supported version to 23. S

Quit Firefox, vi into pentadactyl.xpi in your profile, edit install.rdf inside the xpi file (it's just a ZIP file) and modify the max supported version to 23. Save the install.rdf file, quit vi and start Firefox. Pentadactyl will work, with some minor regressions (e.g. Google home page search box now steals focus) and 's' (google search) command prints error message: Error: TypeError: keywords in null, but the search works. But otherwise everything else seems to work.