firefox alert window

Hello,

In Firefox I have an alert window when I ask again too quickly to check 
the mail accounts (something like "please wait the end of the process"). 
This window seems to block the mail checking, before I press OK. Does it 
have to? Shouldn't the mail checking continue - or be done a second time 
after the first one ends, without blocking the process? Could a message 
in the status bar be enough?

Thanks