While digging up info for bug 1375585, I ran into a problem.

Try to find the patch that added this line:
https://searchfox.org/mozilla-central/rev/b8fbb6ead517720daf0b0211115f407b4b951c74/dom/canvas/WebGLContext.cpp#315

SearchFox's blame bar (after ignoring a reformat cset) thinks it's:

Bug 1164970 - Implement failIfMajorPerformanceCaveat. r=jgilbert, r=ehsan
Kyle Fung <kfung@mozilla.com>, Thu, 21 May 2015 11:51:49 -0400

Local git-blame (after skipping to before the reformat) shows it was actually:

$ git show 10b555b6ab160d
commit 10b555b6ab160d87a92e74e9a983d1a3a8b76eef
Author: Michael Smith <michael@spinda.net>
Date: Thu Jun 22 10:13:12 2017 -0700

Bug 1373739 - Disable WebGL in headless mode. r=bdahl

Yeah unfortunately the skipping-reformat code isn't that great, we have a number of bugs filed against it.

As I'm sure you're already aware, with bug 1632951 fixed you can get the correct result by click on the "show latest version without this line" link on the reformat cset and then searching for the line again.

Bad news: "Show earliest version with this line" doesn't work either.

(In reply to Kartikaya Gupta (email:kats@mozilla.com) from comment #1)

Yeah unfortunately the skipping-reformat code isn't that great, we have a number of bugs filed against it.

As I'm sure you're already aware, with bug 1632951 fixed you can get the correct result by click on the "show latest version without this line" link on the reformat cset and then searching for the line again.

Ah, ok! Yes skipping to "show latest version without this [reformat]" then works, thanks!

We removed the "hyperblame" functionality from searchfox in bug 1673468, so this should no longer be an issue.