Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).

If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:

• In Firefox 29.0 and above, click the menu button , click Help and select Restart with Add-ons Disabled.
• In previous Firefox versions, click on the Firefox button at the top left of the Firefox window and click on Help (or click on Help in the Menu bar, if you don't have a Firefox button) then click on Restart with Add-ons Disabled.

If Firefox is not running, you can start Firefox in Safe Mode as follows:

• On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
• On Mac: Hold the option key while starting Firefox.
• On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
  (you may need to specify the Firefox installation path e.g. /usr/lib/firefox)

When the Firefox Safe Mode window appears, select "Start in Safe Mode".

If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.

To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.

When you figure out what's causing your issues, please let us know. It might help others with the same problem.

el_passo said

I have an issue with Facebook chat emoticons. They simply are not displayed by Firefox. I've reviewed a number of posts all over the Internet related to this issue - no solution. I've tried installing the newest graphics driver, clearing cache, clearing cookies, checking if the emoticons are not blocked content. Could someone help me?

Bug is triggered by hardware acceleration - when I turn off hardware acceleration Firefox shows emoticons normally.

https://support.mozilla.org/en-US/questions/1053941

Can you attach a screenshot?

• http://en.wikipedia.org/wiki/Screenshot
• https://support.mozilla.org/kb/how-do-i-create-screenshot-my-problem

• Use a compressed image type like PNG or JPG to save the screenshot
• Make sure that you do not exceed the maximum size of 1 MB

Missing icons can be supplied by a font that is downloaded from the server (@font-face) as you might see by little boxes that show the hex code of the characters instead.

Make sure that you allow pages to choose their own fonts.

• Tools > Options > Content : Fonts & Colors > Advanced: [X] "Allow pages to choose their own fonts, instead of my selections above"

You can check the gfx.downloadable_fonts.enabled pref on the about:config page and make sure that it is set to true (if necessary double-click the line to toggle its value).