These results look pretty encouraging as to the general quality of the various browsers, until you read the fine print: "Only security bugs were counted in the results (doing anything else is tricky as some browser vendors fix non-security crashes while some don’t)." So, the numbers they show don't count random crashes, never mind incorrect behavior.

And who'd have thought that some vendors aren't even interested in fixing "non-security" crashes; I wonder which vendors those are? And I wonder how many "non-security crashes" their fuzzer found in each browser?

Even worse, they laud MS for the MemGC technology they use in their browsers, but MemGc is just a last-minute hack to try to keep use-after-free bugs from being security holes (by ignoring frees to anything that still has a pointer to it), without having to actually fix them. So, lots more bugs that really ought to crash instead go on to other undefined behavior, which hopefully doesn't amount to a security problem (never mind simply incorrect behavior).

So, it seems that their fuzzer is finding lots and lots more bugs, and they're just not telling us how many there actually were. Maybe the title should indicate better that they're limiting themselves to security vulnerabilities. I suppose there's a call for that sort of measurement, but it would be nice to also hear about the general quality of the software under test. The notion that they'd rate a browser that did exactly nothing as having a 100% perfect rating of zero bugs kind of rankles.