This is something that has been bothering me for a while now. In the past, I was patching appstrings.properties, replacing Firefox with Iceweasel (guess why? ;) ). Recently, I changed that to use the MOZ_APP_DISPLAYNAME build variable, but I'm not sure it plays well with the l10n stuff. I'm attaching that patch for reference. This actually has more impact than on Iceweasel. For instance, previously with Minefield, and now with Nightly and Aurora, you get inconsistent network error messages. For example, if I go to http://localhost:1234 with a Nightly, this is what I can read: Firefox can't establish a connection to the server at localhost:1234. (snip) If your computer or network is protected by a firewall or proxy, make sure that Nightly is permitted to access the Web. For the record, a while ago, I attempted to generically fix this using numbered parameters in the strings, as these strings are actually being formatted in the netwerk code, using parameters. For compatibility purpose, I tried to keep the current parameters at the same index, but it turns out that the formatting code doesn't like formatting strings with, e.g. %3$S when there is no %2$S in the string. By the way, it looks like the application name is actually now passed as 3rd parameter, cf. the externalProtocolPrompt string. So maybe a solution would be to fix the formatting functions to allow %3$S when there is no %2$S in the format string, and replace Firefox with %3$S ?