Yeah, the ctrl-click to select multiple emails for moving or deletion is annoying when it opens a firefox tab for every email.
Also, if you do a shift-click to select a range of emails, it will open the first email in its own firefox window. Thankfully, it doesn't open all of the emails that were shift-click selected.
And apparently, it does this in IE7 tabs also. A bit annoying. Especially the first time I did this and had 10 extra tabs in firefox with each email open that I didn't notice until later.