Appears to be happening for me when I have the Personal Menus extension installed.

https://addons.mozilla.org/en-US/firefox/addon/personal-menu/

Once I removed the extension, the awesome bar and menus show up again.

Edit: Nope, after using it for a little bit that still doesn't fix it. Frank_Geppert's solution of turning off hardware acceleration seemed to work for me though.

Tools -> Options -> Advanced tab -> General tab -> uncheck "Use hardware acceleration when available"

I've seen something similar on OS X if the Firefox window is on the secondary display, the Right Click->Open link in new Window command seems to be broken.

It opens the Window in Firefox memory and it shows up under the windows menu, but it's not displayed anywhere.

This option does work when the Firefox window is on the main display.

I have the same problem and I got rid of it by disabling the hardware rendering acceleration in the settings dialogue. Now I can see the menu from Firefox properly on primary and secondary monitor.

Getting rid of the hardware rendering acceleration in the settings solves the problem.

To clarify, this is not disabling hardware acceleration for the display driver itself (which you probably can not do under Windows 7). You need to disable hardware acceleration within the Firefox options.

I also had similar problems. Had to do two things. Disable hardware acceleration as stated above, and disable the FoxTab add-on. So far, this seems to have solved the problems.

Sadly, disabling hardware acceleration did not do the trick for me. :( I disabled every add-on and plugin, started in safe mode, made a new profile but still no luck. Same problem with 5.0, so it's back to 3 for me.

Had similar issues, particularly when popping up the bookmarks menu. Disabling hardware acceleration worked for me. This is on windows 7, using FF 6; but i've seen it on all versions of FF after 3. Things were fine on the 1st monitor, not the 2nd.

I used a clean profile and still had the issue.

Just for FYI... Firefox>Options>Advanced>General>Browsing

I have same issue. Update FireFox towards 8.0.1 Have 2 screens, working with Ultramon and have Win7 as OS.

Does not matter on which screen my FF is, the option "open in a new window" does not work, what ever i do.

- Disabled hardware acceleration - Personas add-on removed - FoxTab add-on removed

Also without UltraMon installed FF does not let me "open in a new window" Open in a new tab is no issue, but want to have more screens open with their own tabs.