Bug 41542: Disable the creation of a default profile

Firefox creates a profile as a fallback for old versions.
However, we do not need this, so we want to prevent Firefox from
creating the related directories.

We comment out the code, but should Mozilla be interested in a
compile-time flag, we could rewrite the patch to add one.

See also https://bugzilla.mozilla.org/show_bug.cgi?id=1770174.

toolkit/profile/nsToolkitProfileService.cpp

@@ -1578,6 +1578,12 @@ nsresult nsToolkitProfileService::SelectStartupProfile(
 
     rv = CreateDefaultProfile(getter_AddRefs(mCurrent));
     if (NS_SUCCEEDED(rv)) {
+      // tor-browser#41542: We do not need to support legacy versions.
+      // For now, we just use an ifdef, but we could write a patch to disable
+      // this behavior through a build-time flag, should Mozilla be interested
+      // in taking it.
+      // See also https://bugzilla.mozilla.org/show_bug.cgi?id=1770174
+#ifndef BASE_BROWSER
       // If there is only one profile and it isn't meant to be the profile that
       // older versions of Firefox use then we must create a default profile
       // for older versions of Firefox to avoid the existing profile being
@@ -1589,6 +1595,7 @@ nsresult nsToolkitProfileService::SelectStartupProfile(
                       getter_AddRefs(newProfile));
         SetNormalDefault(newProfile);
       }
+#endif
 
       rv = Flush();
       NS_ENSURE_SUCCESS(rv, rv);