Firefox is a brand present in a highly competitive market. It's a brand known by consumers who are used to associate a name and a logo to an experience and can easily get confused (such as people seeing the "blue E icon" as the way to "start google" for instance).

Mozilla protected more agressively its Firefox brand to cope with malware-stuffed clones which were hijacking the name.

Projects such as VLC or Android protect their brand too, Chrome is only available through official closed-source builds, many linux distributions only package chromium.