Apparently Firefox 29 had some major feature or something. I don’t know much about that. What I do know about is a new Firefox feature that will finally cause Firefox to beat Chrome once and for all. Yes ladies and gentlemen, I am talking about a revolutionary feature I’ve dubbed:

Scheme typo fixer-upper™©

Have you ever copy and pasted URLs into the location bar and seen this screen instead of the page you wanted?


Of course you have. So you double check the URL and go “ooooooooh, I missed the h in http when copying and pasting.” Stupid me. Well, at least Firefox gave me an obtuse message to tell me what is going on. How lovely.

So, this happened to me one too many times. And I got pissed. And I had a conversation with my browser. I was probably drinking so it made sense at the time. The conversation went something like this:

WTF Firefox. You KNOW what I meant. Stop being a dick and just do the right thing™.

And then it reminded me of one of the very first “cool” things I experienced at Facebook. Facebook uses Phabricator and Arcanist for their development workflow. Arc (like Mozilla’s Mach) is a local tool to run builds, send up diffs, manage patches, and things of that persuasion. One of the things you do with arc is run

<em>arc build</em>


Well guess what happened. My first day at Facebook I typed

<em>arc biuld</em>

instead of

<em>arc build</em>

. I’m such an idiot. They should have fired me. Much to my delight I saw this:


It says:

And it hit me. Someone was THINKING. They encountered this problem, thought about how many people would do that typo, realized there was really only one possible intended result, and decided to have the computer just do the right thing™. Someone cared about engineer time so much they fixed it for every future engineer to come. The thought and whimsical message made such a large impression on me I insisted we add a similar feature to Buck, Facebook’s super-fast Android build tool:

It uses Levenshtein distance to figure out what you really meant to type. Humans: 1, machines: 0. Sweet.

So right about here I am likely supposed to point out Facebook (and specifically my team) is hiring. Cool, I’ve now done my duty as a manager–that should keep the recruiting attack dogs at bay.

Where was I? Oh yeah, man over machine. So I started thinking, which is never a good thing. This sort of thing happens to me every day and slows me down a lot. For example, if I type

<em>git cone</em>

instead of

<em>git clone</em>



It says:

You know DAMN WELL what I meant git, and you mock me by echoing it out right in front of me. You spit in my face and just sit there all smug about it. What a dick.

So I went to teach git some manners, and it turns out the feature is already there. If you set help.autocorrect git will do the right thing™. There was a bug about making it default but I lost interest reading it to figure out why they insist on making humans do the work of computers. As an aside, do you know the git developers only take contributions as patches to a mailing list? Coding like we’re in the 90s, whooooooo!

Get. To. The. Point.

What does this have to do with Firefox you might ask? What, you don’t like my stories? Fine! Remember the screenshot at the beginning:

I started thinking how stupid Firefox was being, how many wasted human-hours were spent reading the message and acting on it, and how much goodwill Firefox loses when its users roll their eyes at this screen.

And it made me angry. So I decided to fix it. How hard could it be? Alcohol may have been a factor in my difficulty calculation. But I did it! The proof is a screenshot of Google:


I typed in “ttps://” and was taken to “” automatically without seeing an error screen! Firefox will now fix all these typos:

Humans: 2, machines: 0.

Err, ok, this feature doesn’t screenshot well. Just trust me it works. But you probably don’t trust me. I wouldn’t. Try it yourself in any flavor of Firefox > 29! Go ahead, I’ll wait.

Did it work? Of course it did! Oh damn, you tried “hptts” and it didn’t get fixed? My change only deals with dropped characters and not jumbled character typos. It’s not a bug because I documented it™. To be honest I am lazy and lost interest after I fixed my copy and paste pain but it would be trivial to extend my patch to cover the latter case. Get in touch and I can mentor you! Take a look at the code (part 1, part 2). And there are tests! I mainly wrote those to not be a hypocrite as I preach the unit test gospel to product engineers every day. Oh, and for “quality”.

Turns out this life-changing feature was a lot more involved than expected, for two reasons.

First, I naively assumed there would be one location where everything gets loaded from the location bar input. To me that was a sensible way of organizing things. I could then just do a string match on the URL scheme and replace it with the right stuff…easy peasy, right? Errr, no. Turns out Firefox is…interesting. And on a lot of platforms with different UI code.

I kept digging deeper in the stack and when I got to where I needed (docshell) it wasn’t the right place for the fix at all. I’d potentially break web compatibility. Whoops. Rather than doing a simple fix at a lower-level chokepoint I needed to patch in optional support to that low-level and then hunt down every place Firefox takes in URLs and do the typo fixup. And then of course my first patch didn’t work due to a last-minute change and I had to fix things up in a second patch. See the gory details in the bug.

Second, Mozilla’s current setup is very developer-hostile. And that isn’t just “OMGWTFBBQ why isn’t Firefox on teh GitHubz!” and “lke dis if u cry evry tme u tuch c++”. Seriously, I do not know how Firefox developers get any work done. I would quit if I was forced to work on Firefox code all day. I’m not talking about code quality, I’m talking about supporting stuff–from build times, to no linters, to crufty code-search tools, to horrible code review, to dealing with no CI. I think I’ve been spoiled at Facebook as we invest heavily in speeding up the development workflow (we’re hiring!). I have more thoughts on this I intend to blog later, but to my Mozilla friends it doesn’t need to be like this. Expect more from your tools and development workflow!

Ahem. I’ll get off my soapbox and save my fire and brimstone tools talk for another day.

El fin.

Please enjoy the best feature Mozilla has shipped since Firefox 1.0 – the Scheme typo fixer-upper™©! If you encounter problems feel free to file bugs on me and I will promptly ignore them.

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