When Firefox 3.6 detects a network connection issue, it switches to offline mode.
I find it rather annoying as it forces me to manually switch to “online” mode via the file menu each time I replug my laptop.
This behavior can be disabled via a hidden preference.
Type about:config in Firefox address bar, right click to add a new Boolean key and create
network.manage-offline-status
set it to false
Alternatively you may add an extension for this: https://addons.mozilla.org/en-US/firefox/addon/13152/