Question: Whenever I format my computer, I usually just copy/paste all the .ttf and .fon files into the `Fonts` system folder.

I can't be sure 100%, but I think that after I did that, Firefox stopped displaying some website's fonts correctly, and I mean the usual default ones, like Arial, Helvetica, etc.

I don't have this problem in any other program, other than Firefox.

Here is a screenshot of what [Digg](http://en.wikipedia.org/wiki/Digg) looks on my laptop right now:

[![enter image description here](https://i.stack.imgur.com/Zph9q.png)](https://i.stack.imgur.com/Zph9q.png)

It looks weird, the font is messed up somehow.

How do I fix it? I'm on Windows 7, Firefox 3.6.10.

Answer: 
This specific problem is due to installing a version of the Helvetica font (very commonly used on the web) that either Windows or Firefox can't display. To confirm, all you have to do is paste the following text in your Firefox address bar and hit enter:

```
data:text/html,
Helvetica
   <font face="Helvetica" size="25">abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ</font>

Helvetica Neue
  <font face="Helvetica Neue" size="25">abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ</font>

```

If it displays as weird symbols, then you can be sure that's your problem.

To fix it, all you have to do is go to %WINDIR%\Fonts and delete all the fonts named Helvetica.

If for some reason, Windows doesn't allow you to, you have to go to the registry, navigate to `HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Fonts` and then delete all the entries that have Helvetica on their name.

If you are using Windows 7 64-bit, you also have to delete the Helvetica entries from the following registry key.

```
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Windows NT\CurrentVersion\Fonts

```

After this, you only need to reboot your computer and the fonts will be displayed correctly again. At least that fixed it for me.
Go to your firefox preferences, under the "Content" tab there should be a "Default Font" combobox. Try switching the setting to one of the usual Microsoft fonts. If not, it is possible that you simply don't have the Microsoft fonts installed. Apparently, you can get some of the core fonts here: <http://web.nickshanks.com/fonts/microsoft-core-web-fonts>