ICU 75 requires C++17 mode as a bare minimum.

--- Arctic-Fox-45.1/build/moz.configure/toolchain.configure.old	2024-09-30 14:54:44.000000000 -0500
+++ Arctic-Fox-45.1/build/moz.configure/toolchain.configure	2024-11-19 00:21:31.792210428 -0600
@@ -339,9 +339,9 @@
     # Note: MSVC, while supporting C++11, still reports 199711L for __cplusplus.
     # Note: this is a strict version check because we used to always add
     # -std=gnu++11.
-    if info.language == 'C++' and info.language_version != 201103:
-        if info.type in ('clang-cl', 'clang', 'gcc'):
-            append_flag('-std=gnu++11')
+    if info.language == 'C++' and info.language_version < 201703:
+        if info.type in ('clang', 'gcc'):
+            append_flag('-std=gnu++17')
 
     # We force clang-cl to emulate Visual C++ 2013 Update 3 with fallback to
     # cl.exe.