Bugzilla

Perhaps the file isn't being processed near https://searchfox.org/mozilla-central/source/moz.configure#948

There is new code in mozilla-central/moz.configure and a local test does show it calling helper.add with MOZ_APP_PROFILE=thunderbird

```
+@depends(build_environment, build_project, "--help")
+@checking("if project-specific confvars.sh exists")
+# This gives access to the sandbox. Don't copy this blindly.
+@imports("__sandbox__")
+@imports(_from="mozbuild.configure", _import="confvars")
+@imports("os.path")
+def load_confvars(build_env, build_project, help):
+    confvars_path = os.path.join(build_env.topsrcdir, build_project, "confvars.sh")
+    if os.path.exists(confvars_path):
+        helper = __sandbox__._helper
+        # parse confvars
+        try:
+            keyvals = confvars.parse(confvars_path)
+        except confvars.ConfVarsSyntaxError as e:
+            die(str(e))
+        for key, value in keyvals.items():
+            # FIXME: remove test once we no longer load confvars from old-configure.
+            if key in __sandbox__._options:
+                # ~= imply_option, but with an accurate origin
+                helper.add(f"{key}={value}", origin="confvars", args=helper._args)
+        return confvars_path
```