Pentadactyl: how to disable menu bar toggle by <Alt>?

Using Pentadactyl, when I press the Alt key, it toggles the menu bar, and the --MENU-- mode. This is very embarrassing for me, as I use dwm window manager at the same time, where Alt is the most important meta key, so I hit it very often. How can I disable Pentadactyl's behaviour? I mean, I want it to do nothing when I press Alt. I already tried to remap Alt or Meta to nothing:

:map <A> <Nop>
:map <M> <Nop>

But it doesn't work.

Summary: in about:config, toggle ui.key.menuAccessKeyFocuses to false.

Actually recently this is the normal behaviour of Firefox. Recently, because few versions earlier it was not like this. And using extensions like Pentadactyl or Vimperator, it is very apparent and annoying, while possibly with the default user interface it's convenient. So I searched for related Firefox settings, and I found, the ui.key.menuAccessKey and ui.key.menuAccessKeyFocuses. First I had the intuition that the first needed to change, which was set to 18, which means the Alt key. I set it to 0, without any effect. Then I changed the latter, from true to false, and the issue become resolved.

Nice, the Alt will not toggle the Menu bar with my Iceweasel (Firefox) on Debian 7.

$ vim ~/.pentadactylrc
...

set guioptions=BNs

"  - Disable Alt key to toggle hidden Menu bar for Debian, Ubuntu.
set guioptions-=m
set! ui.key.menuAccessKeyFocuses=false

...

1. the set! ui.key.menuAccessKeyFocuses=false need to after the set guioptions-=m.

2. Here is my patch - [issue #6] Disable menu bar toggle by for Pentadactyl · chusiang/tuxENV@b4a7279.

Seeing as you're using dwm it might suit you better to just remap dwm's MODKEY, I prefer using the super, or "windows", key for this.

see this link for how to and a list of modkeys you can use.

It's preferable this way as a lot of applications like to map ALT.