I have Dropbox installed on my Ubuntu desktop 12.10, I also have Firefox and Chrome installed. Chrome is my default browser, I have checked in my mimeapps.list and its all correct. Yet for some reason the integration of Dropbox opens Firefox when I use the "Launch Dropbox website" option from the menu, is there a file somewhere this is looking at as I would like it to open in Chrome which I mostly have already running than launching a new instance of Firefox? Or could this be a Dropbox bug?
I had similar problem with my Xubuntu 13.04 and I solve it with this commands.
So you just need to select the browser you want to use, in my case its chromium-browser, so I entered number
Dropbox is still a gtk2 application while Unity and current Gnome are on gtk3. Gtk2 applications store their settings in gconf instead of dconf. Maybe they got out of sync.
Edit the following key:
with the gconf-editor user interface (available as package) or with gconf command:
Last not least there are the debian alternatives system, use package
It is also possible that dropbox keeps the browser that it encountered during install, in this case please report the bug.