Many site issues can be caused by corrupt cookies or cache.

• Clear the Cache and
• Remove Cookies

Warning ! ! This will log you out of sites you're logged in to. You may also lose any settings for that website.

• Cookies; Delete cookies to remove the information websites have stored on your computer {web link}

• Cache; How to clear the Firefox cache {web link}

If there is still a problem, Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Did this help?

While you are in safe mode;

Try disabling graphics hardware acceleration in Firefox. Since this feature was added to Firefox it has gradually improved but there are still a few glitches.

How to disable Hardware Acceleration {web link}

I tried all of these, and tried refreshing Firefox, and it still does not work.

Start your Computer in safe mode with network support. Then start Firefox. Try Safe websites. Is the problem still there?

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia

Note that with an unstable (alpha) Nightly build things can go wrong at any time.

Best is always first to try a new profile and possible check out the daily threads at the mozillaZine Builds forum to see if there are known issues.

Make sure you have a version of the current Firefox release available with its own profile. Using the same profile with Nightly and other releases is asking for trouble.

• https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles