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.

You can check for corrupted and duplicate fonts and other font issues: http://www.thexlab.com/faqs/multipleappsquit.html - Font Book 2.0 Help: Checking for damaged fonts http://www.creativetechs.com/iq/garbled_fonts_troubleshooting_guide.html

Sorry but above answer doesn't solved my problem!!  :(

Some of your crash reports weren’t sent to the Mozilla Servers.

In the address bar, type about:crashes<enter>. Note: If any reports do not have BP in front of the numbers/letters, click it and select Submit.

The crash report is several pages of data. We need the report numbers to see the whole report.

Using your mouse, mark the most resent 7 - 10 crash reports, and copy them. Now go to the reply box below and paste them in.

• see if there are updates for your graphics drive drivers

https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration

• disable protected mode in the Flash plugin (Flash 11.3+ on Windows Vista and later)

https://forums.adobe.com/message/4468493#TemporaryWorkaround

• disable hardware acceleration in the Flash plugin

https://forums.adobe.com/thread/891337 See also:

• http://kb.mozillazine.org/Flash#Troubleshooting

You can right-click and select "Inspect Element" to open the Inspector (Firefox menu button or Tools > Web Developer) with this element selected. You can check the font used for selected text in the Font tab in the right pane of the Inspector.

• https://developer.mozilla.org/Tools/Page_Inspector

Nothing has worked, even it is getting worst. Now most of the fonts looks like this damaged. Please help me to short it out. I uninstall firefox several times but still facing the same problem after re-installing.

What font(s) is Firefox using?