This could be several things. Please try these and report back

Type about:preferences#content<enter> in the address bar. Across from fonts and colors, press the Advanced button. On the bottom, turn on Allow Web Sites To Choose Their Own.

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.

Type about:preferences<Enter> in the address bar.

• Cookies; Select Privacy. Under History, select Firefox will Use Custom Settings. Press the button on the right side called Show Cookies. Use the search bar to look for the site. Note; There may be more than one entry. Remove All of them.
• Cache; Select Advanced > Network. Across from Cached Web Content, Press Clear Now.

If there is still a problem, Start Firefox in Safe Mode {web link} While you are in safe mode;

Type about:preferences#advanced<Enter> in the address bar.

Under Advanced, Select General. Look for and turn off Use Hardware Acceleration.

Poke around safe web sites. Are there any problems?

Then restart.

I did everything except turn off the HW accelerator. Now the menu items show up!

Thanks.

Good to hear, Safe surfing.

Missing icons are usually 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.

• Firefox > Preferences > 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).