One of the things we've mentioned a few times since somewhere in the 2.0 cycle is switching nibs over to GTMUILocalizer, starting with a few key nibs that aren't layout-sensitive.
This would allow us to do things like fix bug 525758 without resorting to a nasty hack since we were well past string freeze, and also keep improperly-updated-by-l10n-tools BrowserWindow and MainMenu nibs from horking the browser, rendering bookmarking non-functional, and similar things we've seen. It would also let us do things like turn them into compiled xibs (presumably for speed, but also to prevent casual hacking).
This bug is a P? on the 2.1 list, meaning "Priority to be determined." It's a definite want, so P2 for MainMenu and BrowserWindow (up to beta 1/l10n freeze), P3 for other nibs.
(This is also part of our long-term single-binary l10n strategy: http://wiki.caminobrowser.org/User:Sardisson/Towards_a_single_Camino_binary#Make_nib_changes_not_require_localizer_changes_to_prevent_breakage )
Apparently we can't use Apache-licensed code, which is what GTM is (this is based on news stories about how Mozilla hopes to update the MPL by the end of 2010, and one of the things they are looking at is making it Apache-compatible). So I don't think we'll be doing this for 2.1 :(
We could if we shipped under the GPL or LGPL instead of the MPL/tri-license, I bet...
All code in the tree has to be compatible will all three of the tri-license's licenses (see bug 495620, where we had a GPL-incompatible license), so, no, I don't think we can get around that.