diff --git a/.hgtags b/.hgtags
index 6de44e4d78d2..35eaa3c3e9ef 100644
--- a/.hgtags
+++ b/.hgtags
@@ -5089,3 +5089,4 @@ c4a5d008ee64fab523384408fa2868e2d028025d FIREFOX_128_4_0esr_BUILD1
 c4a5d008ee64fab523384408fa2868e2d028025d FIREFOX_128_4_0esr_RELEASE
 68352da82b95d7114af99b268c179195fd2fead0 FIREFOX_128_5_0esr_BUILD1
 68352da82b95d7114af99b268c179195fd2fead0 FIREFOX_128_5_0esr_RELEASE
+a6cdcd2ed9ec3e256f358010672bafd1674b0b8b FIREFOX_128_5_1esr_BUILD1