For testing purpose I tried to switch to offline mode (File > Work offline), and upon refresh, it showed "Firefox is currently in offline mode and can't browse the Web."
When I clicked "Try Again" it went back "Online" again.
How can I work offline to see how my app performing offline?
First check your settings for Firefox.
In Ubuntu, go to
Edit > Preferences > Advanced > Network
Under Offline Web Content and User Data, see how much space is used by Firefox.
If it shows
"Your application cache is currently 0 bytes of disk space",
0 bytes
it probably means you disabled the Firefox offline cache.
Type "about:config" into the address bar and hit Enter, then click the "I'll be careful, I promise!" button and search for these values:
browser.cache.disk.enable user set boolean false
browser.cache.memory.enable user set boolean false
Please refer to Mozilla Firefox support before you do something there.
If you are using Firebug, that you may have enabled the Disable Browser Cache option within the Net Panel. Disable that option and try again.
Another issue you may get with FireQuery, If you see something like
TypeError: this.__FireQueryShared is undefined
remove FireQuery add-on and try again.