[Osiris]

Source: Linux Solutions: Why does Firefox start in offline mode?

If you have this problem you know how frustrating it can be. Every time you fire up Firefox it wants to start in offline mode. To get around this you have to go to the File menu and uncheck the Work Offline box.
When I first encountered this I immediately opened up about:config and searched everywhere for the entry that was causing this issue. No luck. Every possible entry “browser.online” entry was checked as “true”, but still the browser would start offline. Everywhere I looked it seemed it was set up properly…and this shouldn’t be a difficult issue. It was turning into a hair-losing situation. Eventually, however, I would figure out what was going on.

[Logarithms]

I actually don't have that problem. However, it happens to a friend of mine.