CVE-2025-1933 is a high severity vulnerability in Firefox's Just-In-Time (JIT) compiler for WebAssembly (WASM) on 64-bit CPUs. The JIT compiler can incorrectly handle i32 return values by including bits from leftover memory, potentially causing these values to be treated as a different type. This flaw affects Firefox versions prior to 136 and Firefox ESR versions prior to 115.21 and 128.8. The issue was fixed in Firefox 136 and the corresponding ESR releases.