I think what madref wants is a list of browsers rather that the default or user chosen browser. I suspect that might be hard.
On Linux, you can search for installed packages under the Section "World Wide Web", that will pick up Firefox or Google Chrome on my Ubuntu install for example. But also wget and will not pickup Konqueror. Hmm...
What if user has decided to manually install Vivaldi ?
Maybe better to search for know binary names. Don't forget many Ubuntu users are now installing Chrome directly from Google because Ubuntu decided to make it available only in a Snap from its repositories. Sigh ...
Not easy.
Davo