The "Work Offline" mode in Firefox can be useful if you don't have an internet connection, but Firefox annoyingly enables it automatically whenever you lose connection, even for a second. Here's how to disable that behaviour.
If you have a spotty connection and are sick of Firefox constantly throwing you into Work Offline mode, there's a new about:config tweak in Firefox 3.6 and above that will disable this annoying behaviour. Type about:config in the address bar, right click anywhere, and hit New > Boolean. Type in network.manage-offline-status as the preference name and hit OK, setting it to false when prompted.
Now, Firefox should stop automatically toggling the Work Offline mode when your connection blips out. Of course, you can still use Work Offline mode, you just have to toggle it yourself in the preferences.