When you are having issue with a particular issue, try to delete cookies first. It solves a lot of problem. To do so just follow these steps:

• Click the ≡ (menu button) and choose Preferences.
• Select the Privacy panel.
• Set Firefox will: to Use custom settings for history.
• Click Show Cookies.... The Cookies window will appear.
  • In the Search: field, type the name of the site (in your case facebook.com). The cookies that match your search will be displayed.
  • Select the cookie(s) in the list to remove and click Remove Cookie.
  • Select the first cookie and press Shift+End to select all the cookies in the list.
  • Click Close to close the Cookies window.

Hope it will work for you.

Many thanks for your help. Unfortunately it doesn't work...tried to remove all cookies. Any other ways?

After some research on internet, it seems that this is a problem with your proxy settings. To do so, follow this steps:

• Go to Preferences
• Then go to Advanced then Network
• Click on the Settings button
• Toggle between these settings. I'm on Windows so not sure what is appropriete for you. May be Use system proxy settings or "No proxy" will work fine.

You can open the Web Console (Firefox/Tools > Web Developer). Check on the Network tab if CSS or other content from a specific domain is blocked and has a file size 0 (zero).

• https://developer.mozilla.org/Tools/Web_Console
• https://developer.mozilla.org/Tools/Network_Monitor

cor-el said

You can open the Web Console (Firefox/Tools > Web Developer). Check on the Network tab if CSS or other content from a specific domain is blocked and has a file size 0 (zero).

• https://developer.mozilla.org/Tools/Web_Console
• https://developer.mozilla.org/Tools/Network_Monitor

Thanks for your help. But it is too complicated for a general user and I have no web developing experience. Please share any simpler way if any. Thanks.

Sashoto Seeam said

After some research on internet, it seems that this is a problem with your proxy settings. To do so, follow this steps:

• Go to Preferences
• Then go to Advanced then Network
• Click on the Settings button
• Toggle between these settings. I'm on Windows so not sure what is appropriete for you. May be Use system proxy settings or "No proxy" will work fine.

Tried. doesn't work. Thanks.

Sashoto Seeam said

After some research on internet, it seems that this is a problem with your proxy settings. To do so, follow this steps:

• Go to Preferences
• Then go to Advanced then Network
• Click on the Settings button
• Toggle between these settings. I'm on Windows so not sure what is appropriete for you. May be Use system proxy settings or "No proxy" will work fine.

By the way, I am running Mac OX Yosemite.

Any thought?