Firefox 3.5.9 is included in OLPC OS 10.1.3 and can be activated from GNOME.
Installing Adobe Flash
Firefox on OLPC OS does not include Adobe Flash plugin, and as a result some web sites do not work as designed. To install the plugin see Adobe Flash, in particular the section for Browse.
See Firefox/Obsolete for a Sugarised Firefox for old OLPC OS releases prior to 10.x.
Firefox can also run from within Terminal. Type firefox at the Terminal prompt and press enter.
Since OLPC OS 10.1.3 is based on Fedora 11, and Fedora 11 security updates have ceased, there are no further updates to Firefox. Deployments who need a more recent version of Firefox should replace the one in OLPC OS as their build is constructed.