hello rafciu1978, thanks for reporting this issue. could you go to the firefox menu ≡ > help ? > troubleshooting information, copy the contents of that page and paste them here into a reply on the forum? this might give us a clue what is going on...

See also this thread:

• [/questions/1027393] Active Tab has floating chinese characters as well as the tab name how do I get rid of this?

You can try to disable the McAfee MSC FF plugin DLL plugin in "Firefox/Tools > Add-ons > Plugins"

If it is caused by a plugin then Safe Mode wouldn't have effect and thus wouldn't get noticed via troubleshooting extensions (plugins are not affected by Firefox Safe Mode).

• https://support.mozilla.org/kb/Troubleshooting+plugins

See also these SUMO threads:

• [/questions/1034427]
• [/questions/1027393]