Sounds as if you are blocking stylesheets. Have you got View > Page Style set at "No Style"?

No, it's set at Basic Page Style.

Other sites are displaying fine, it's just that one I'm having issues with.

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.

Thanks. Clearing cache and cookies didn't help, but starting in safe mode did. Looks like one of my add-ons is causing the problem. Appreciate the help.

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All of them.