@voxel @torproject You should search our forum and find one of many cases we've given lots of details about it.
Firefox has a far weaker sandbox without complete site isolation support. On Android, they have no sandbox at all, not even a basic content sandbox. They have drastically weaker exploit mitigations with nothing comparable to Oilpan, MiraclePtr, PartitionAlloc, etc. or the additional layer of sandboxing for JS provided by the V8 sandbox. Far less fuzzing, testing, hardening, etc.