If you’re going to install some fancy graphical web browser, chances are the first plugin you’re going to install with be the Flash plugin so you can view porn videos at youtube.
Unless your fancy graphical web browser is IceCat:
GNU IceCat is the GNU version of the Firefox browser. Its main advantage is an ethical one: it is entirely free software. While the Firefox source code from the Mozilla project is free software, they distribute and recommend non-free software as plug-ins and addons.
Lets be specific here: IceCat isn’t a home-brew Firefox lookalike. It is forked from the Firefox source code.
And the reason for diluting the Firefox marketshare? So that you won’t be offered plugins you can’t obtain source code for (their use of “free” relates to source-code availability, not cost).