"Here it doesn't work, it install but doesn't block anything.
Also happened for a few friends."
Nightly Tester Tools
http://www.all4you.dk/FreewareWorld/links.php?page=60&cat=012
http://users.blueprintit.co.uk/~dave/web/firefox/buildid/nightly.html
This extension adds a few extras useful to those that regularly test
nightly builds of Firefox, Thunderbird and the Application Suite.
This extension now works on branch builds of Firefox and Thunderbird.
Features:
* Allows you to install incompatible extensions (experimental).
* Allows you to force the application to believe an extension is
compatible with the current version and enable it. (Only works on
recent builds of Firefox and Thunderbird, branch and trunk since
20/08/2005).
* Adds a menu item to let you to copy the build identifier to the
clipboard.
* Adds a menu item to let you insert the build identifier into the
current text box.
* Adds a toolbar button to let you insert the build identifier into
the current text box (Not supported in the Application Suite).
* Provides an easy way to launch talkback.
* Lets you customise the title bar to include the build identifier
and other information.