Webmail (IMP H3 4.0.3): Firefox Browser not displaying left menu.

It seems it is a problem with some versions of Firefox and the IMP Java Applet.
If you want to fix things your self, you can tell IMP not to display the menu on the left:

Step # 1 - Open Firefox
Step # 2 -Go to your Webmail http://webmail.yourdomain.com
Step # 3 -Login to Webmail with username and password
Step # 4 -Once logged in, Click on "Options"
Step # 5 -On the "Options" page click : "Edit Options for" and choose Horde in the drop down menu
Step # 6 - Click on "Display Options"
Step # 7 - "UnCheck The Box Where is says " Show the Horde Menu on the left?"
Step # 8 - Important "Click Save" at the bottom of the page.
Step # 9 - Log Out by Clicking "Log Out"

Once you have done that, you should have the menu on the top of your page the next time you log in.