hi genivieve, this is probably caused by microsoft update kb3013455 which can cause font rendering issues on vista:

After you install security update 3013455, you may notice some text quality degradation in certain scenarios. The problem only occurs on systems that are running Windows Vista SP2 or Windows Server 2003 SP2. Microsoft is researching this problem and will post more information in this article when the information becomes available.

^{https://support.microsoft.com/kb/3013455}

You can try to disable OMTC and leave hardware acceleration in Firefox enabled.

• about:config page: layers.offmainthreadcomposition.enabled = false

You can open the about:config page via the location/address bar. You can accept the warning and click "I'll be careful" to continue.

• http://kb.mozillazine.org/about:config

You can try to disable hardware acceleration in Firefox.

• Tools > Options > Advanced > General > Browsing: "Use hardware acceleration when available"

You need to close and restart Firefox after toggling this setting.

• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes
• https://support.mozilla.org/kb/upgrade-graphics-drivers-use-hardware-acceleration