- In the address bar, type "about:config" (with no quotes), and press Enter.
- Click "I'll be careful, I promise"
If you use extensions (Firefox/Tools > Add-ons > Extensions) that can block content (e.g. Adblock Plus, NoScript, Flash Block, Ghostery) then make sure that such extensions aren't blocking content.
Check if this happens in safe mode:
Try clear your recent history:
What should I do once I right click? The entry says, "default" "boolean" "true"