None of those make money selling GPL software. The GPL software undergirds the product they sell, but it is not the product itself.
MySQL: Fancy proprietary version with non-GPL features makes money, GPL version sits there doing nothing. Used to make money from a traditionalist dual-license model before Oracle took over, now they just neglect the GPL version.
WordPress: Makes money from hosting and consulting, not from its software.
Drupal: ibid.
Firefox: makes money from search affiliate deals and charitable donations. This is closer because they make money by getting brands in front of Firefox's installed base, which is sort of close to making money from software, but still indirect.
Android: Google does not make money from Android directly except insofar as they negotiate licensing deals with phone providers for their closed-source "Google Apps" suite and/or for "Google Play Edition" or other official branding on a phone. In these cases, they are selling a collection of Android apps and/or Google branding, not the GPL software that runs on the phone.
I don't know of any case where a company sustained itself on the sales of actual GPL software. Every open-source company lives off ancillary services or licensing deals (dual-licensing like MySQL or branding deals like Google).
MySQL: Fancy proprietary version with non-GPL features makes money, GPL version sits there doing nothing. Used to make money from a traditionalist dual-license model before Oracle took over, now they just neglect the GPL version.
WordPress: Makes money from hosting and consulting, not from its software.
Drupal: ibid.
Firefox: makes money from search affiliate deals and charitable donations. This is closer because they make money by getting brands in front of Firefox's installed base, which is sort of close to making money from software, but still indirect.
Android: Google does not make money from Android directly except insofar as they negotiate licensing deals with phone providers for their closed-source "Google Apps" suite and/or for "Google Play Edition" or other official branding on a phone. In these cases, they are selling a collection of Android apps and/or Google branding, not the GPL software that runs on the phone.
I don't know of any case where a company sustained itself on the sales of actual GPL software. Every open-source company lives off ancillary services or licensing deals (dual-licensing like MySQL or branding deals like Google).