use :Dactyl command to control pentadactyl directly in vim

control_pentadactyl.vim

if (!exists('g:firefox_execute') || empty(g:firefox_execute))
	let g:firefox_execute = 'firefox'
endif
fun! DactylComplete(A, L, P) "{{{
	if (!exists('g:DactylCompleteLoaded'))
		let l:tmp = tempname()
		let l:getListCommands = 'js let hives = modules.commands.allHives;'
			\ .'var names = [];'
			\ .'Array.forEach(hives, function(hive) {'
			\ .'    let lists = hive._list;'
			\ .'    Array.forEach(lists, function(list) {'
			\ .'        names = names.concat(list.names);'
			\ .'    });'
			\ .'});'
			\ .'names.sort();'
			\ .'uniqueNames = names.filter(function(elem, pos) names.indexOf(elem) == pos);'
			\ .'names = uniqueNames;'
			\ .'var localFile = Components.classes["@mozilla.org/file/local;1"].createInstance(Components.interfaces.nsILocalFile);'
			\ .'try {'
			\ .printf('    localFile.initWithPath("%s");', l:tmp)
			\ .'    if (!localFile.exists() || (!localFile.isDirectory())) {'
			\ .'        Components.utils.import("resource://gre/modules/NetUtil.jsm");'
			\ .'        Components.utils.import("resource://gre/modules/FileUtils.jsm");'
			\ .'        var ostream = FileUtils.openSafeFileOutputStream(localFile);'
			\ .'        var converter = Components.classes["@mozilla.org/intl/scriptableunicodeconverter"].createInstance(Components.interfaces.nsIScriptableUnicodeConverter);'
			\ .'        converter.charset = "UTF-8";'
			\ .'        var istream = converter.convertToInputStream(names.join("\n"));'
			\ .'        NetUtil.asyncCopy(istream, ostream, function(status) {'
			\ .'            if (!Components.isSuccessCode(status)) {'
			\ .'                return;'
			\ .'            }'
			\ .'        });'
			\ .'    } else {'
			\ .'        dactyl.echoerr("Unable to save file!");'
			\ .'    }'
			\ .'} catch (e) {'
			\ .'    dactyl.echoerr("failed!");'
			\ ."}"
		sil call system(printf("%s -pentadactyl-remote \"%s\"", shellescape(g:firefox_execute, 1), escape(l:getListCommands, "\"")))

		try
			let g:DactylCommands = readfile(l:tmp)
			let g:DactylCompleteLoaded = 1
		catch
			echoerr "Completion failed, maybe firefox isn't running."
			return []
		endtry
	endif
	let l:args            = g:DactylCommands
	let l:valid_completes = []
	for l:arg in l:args
		if stridx(l:arg, a:A) == 0
			let l:valid_completes += [l:arg]
		endif
	endfor
	return l:valid_completes
endfunction "}}}
" FIXME: :Dactyl echo <></>
" FIXME: let it work on Windows
command! -complete=customlist,DactylComplete -nargs=* Dactyl sil call system(printf("%s -pentadactyl-remote \"%s\"", shellescape(g:firefox_execute, 1), escape(<q-args>, "\"")))

use :Dactyl to run pentadactyl ex commands.

for example:

:Dactyl pwd

You can use 'g:firefox_execute' variable to specify the location of your firefox execute.

Unfortunately, it doesn't work on Windows.

It doesn't work on Mac OS X too.