How can I force ubuntu to use font A instead font B in all applications and web pages?

Question

i am new in linux, my question simply is: how i can force ubuntu to use font A instead font B in all application and web page? for example there is a web page that uses Tahoma Font, but I want my browser use ubuntu font istead tahoma automatically,

Answer 1

I use this content in ~/.fonts.conf to replace several fonts with Ubuntu

<!--?xml version="1.0"?>-->
<!--DOCTYPE fontconfig SYSTEM "fonts.dtd">-->
<!-- ~/.fonts.conf for per-user font configuration -->
<fontconfig>
<alias>
    <family>sans-serif</family>
    <prefer>
        <family>Ubuntu</family>
    </prefer>
</alias>
<alias>
    <family>monospace</family>
    <prefer>
        <family>Ubuntu Mono</family>
    </prefer>
</alias>
<match>
    <test name="family"><string>Arial</string></test>
    <edit name="family" mode="prepend" binding="strong">
        <string>Ubuntu</string>
        <string>Arial</string>
    </edit>
</match>
<match>
    <test name="family"><string>helvetica</string></test>
    <edit name="family" mode="prepend" binding="strong">
        <string>Ubuntu</string>
        <string>Helvetica</string>
    </edit>
</match>

</fontconfig>