I'm on MacOSX. gmail is just a link & if I click it it sends me to gmail. If I control-click (Right-click on Windows) & choose "Open Link in New Window", then it opens a new window.
I'm wondering if the window you open is hidden behind the the main window? Try moving your main window to the side to see if the new window was hidden behind it.
Perhaps try "Open Link in New Tab" instead? This might prove to be more reliable.

Are you using the latest FireFox version? I remember you wanted to downgrade some time ago. Perhaps some earlier FireFox versions will have bugs with using the newer abilities of Google, etc.