I could use a little help from an NSIS expert
In Internet Explorer the user_agent extension are defined by a registry entry (This is e.g. how IE/IIS "knows" that a .net runtime is installed):
HKLM "Software\Microsoft\Windows\CurrentVersion\Internet Settings\5.0\User Agent\Post Platform" "Some funny string"
All entries here end up in the user_agent.
In Firefox it is a little trickier: the following steps are needed:
- Is Firefox installed?
- Locate the profile directory (per user)
- Read the profiles.ini and locate the current user profile
- Look for the file user.js, create it if missing
- Add the line
user_pref("general.useragent.extra.funnySoftware", "Some funny string");if missing



