-> click Firefox button, click Options -> go to Advanced section -> Network -> Offline Storage (Cache): click Clear Now button

Try the following solutions and whichever setting works, keep it Permanent:

1) click Settings... button infront of Connection -> select option1 -> Click OK -> OK

2) click Settings... button infront of Connection -> select option2 -> Click OK -> OK

3) click Settings... button infront of Connection -> select option3 -> Click OK -> OK

Check which solution works.

You can find the connection settings in Firefox > Preferences > Advanced : Network : Connection

The default connection setting is "Use the system proxy settings". If that doesn't work then select "No Proxy"

See "Firefox connection settings":

• https://support.mozilla.com/kb/Firefox+cannot+load+websites+but+other+programs+can