Firefox: Control + Mouse Wheel is the Wrong Way Around (and how to fix it)

It's not that difficult, is it?

The diagram on the right illustrates how things everywhere are. Everywhere except Firefox, that is. For reasons unknown to me Firefox does the exact opposite of what would have been intuitive. I.e. increase the font size with up and decrease it with down. Firefox, however, does it the other way around.

I'm using Firefox for years and I still mix that up over and over again. Today was the first day I became aware of that though. After failing to increase the font size I stopped reading, looked at the mouse wheel, and wondered why it didn't increase the font size. I moved the mouse wheel up, didn't I?

I moved it up indeed, but Firefox didn't meet my expectations. "Up" equals "more" and "forward" means closer to the screen, which also equals bigger font sizes. No matter how I look at it there doesn't seem to be any explanation for the observed behavior.

Fortunately there is a way to undo this inversion: change the value of mousewheel.withcontrolkey.numlines (over in about:config) to "-1". After doing that Firefox behaves like any other program. Great. Well, the name of that variable doesn't make much sense, but it really is the right one.

I wonder why they are shipping Firefox with this nonsense default behavior. It really doesn't make any sense, does it? Ah well, at least it's easy to fix.


Firefox 3

A very interesting thought. In Firefox 3 Beta 4 it’s fixed … when you move the wheel up, you see everything larger. So it’s as you would expect.

That's good to hear

I recently uninstalled some outdated FF3 beta and I was too lazy to download a newer one. I just assumed FF3 would behave the same. Well, it's cool that FF didn't meet my expectations in this case. ;)


Maybe the developers thought that scrolling down would mean: "Hey page, come closer to the user's eyes", as you were asking someone with the finger to come closer. When I was a kid we called that the Silence Game. And if someone come closer to you, you actually see him bigger :)

I can agree it is not standard, but do not mention intuitivity here, since different metaphors invalidate the sole intuitivity as a usability metric, IMHO :)

Regards, Antonio


Ye, if we all had psycho kinetic super powers that would make a lot of sense. ;)

Edit: To clarify things a bit... "intuitive" are things you are used to or things you can put into some known context. "Intuitive" doesn't mean that you can use a program right away. There aren't programs like this. Well, maybe one day with the magic of brain interfaces.

In all programs I know the mouse wheel acts as I explained. Additionally, your example doesn't fit the existing model. Just take scrolling... if you scroll down (mwheel down) you move the view down (the page goes up). So, that kind of explanation doesn't really work if you take the most common mouse wheel task into account.

Panning the canvas around (instead of the view/viewport/pov) is rather exotic. Only a few programs use this kind of interaction and I would also guess that more than 50% of the users never did anything like that. Well, a few of em perhaps... by accident... in a PDF viewer. But generally it's really something most casual PC users haven't ever used. Most people don't use vector drawing programs, CAD software, map editors etc. So, they really aren't used to moving the world around 'em.

It isn't about metaphors, really. It's about conventions and abstract concepts most users aren't aware of. Those metaphors can only explain possible reasons (and/or act as brain hooks) for those conventions.

psycho kinetic

Well, you know, mozilla people do have psycho kinetic super powers.

Bye, Antonio


Yes, I agree with your points.
I was only trying to guess the devs mind for that behaviour, that's all. You see, mine was a neutral comment.

If not about metaphors we can speak of Point of Views, Firefox "moved the world" while we are used to "move ourselves".

As you said, a CAD designer is the creator of "his world" so panning around make he feels like god, normal users are just human, so they take the "burden" to move themselves around the "world", scrolling the page down means: "let's bring our eyes down the page"; so different users have different intuitivity, maybe it's driven by their needs, desires, beliefs or expectations, that's what I was trying to say.

But, again, if we put on our soft.eng. hat, and consider intuitivity under a statistical umbrella, then my consideration is useless again :)
All in all, we can say that we are happy they fixed the behaviour in FF3.

Bye, Antonio


I'm also glad that they fixed it.

But I'm still puzzled why it took me so long to notice it. I always scrolled the wheel into the wrong direction first and then change the direction. I always subconsciously adjusted my input without paying attention. It's sorta odd, but I guess the reason for that are similar issues in all kinds of programs. So, basically I'm just used to random screw-ups in random places.

That's probably one of the reasons why it's so difficult to identify usability issues. We are doing so many things routinely that we don't pay attention to pointless extraneous steps.

One of my favorite usability breakthroughs are the index finger marker nubs on keyboards (those on the 'F' and 'J' keys). It's pure genius. Whoever identified this issue... I salute to your awesomeness. Altogether it must have saved several centuries of time, which would have been wasted with looking at the keyboard and hitting backspace.


Well, Firefox is not the only application that got it the wrong way around. Many modern FPS games have MWheelUp assigned to "previous weapon" and MWheelDown to "next weapon" as a default. That's a thing I never understood.


In PK it's the other way around. Up is next and down is previous.

A friend just told be that it was the wrong way around in Quake3 (he changed it immediately). I can't verify that myself right now though.

Well, using prev/next is for newbs anyways. ;)


Actually I like it that way. Always had "next weapon" on mwheel down and "prev weapon" on mwheel up in games.
I guess because I read from top to bottom and would sort numbers like from 1 at the top to 5 at the bottom. So next weapon is "weapon +1" = "weapon in the next line" = "down".
For text resizing I feel this is correct too as the characters get "stretched", I "pull" them down. When I make fonts bigger the text moves down so naturally I connect "down" with "bigger text" in my mind.

I really think that this is the right way. After all I use the mousewheel as wheel and not as "button labelled 'up'" and "button labelled 'down'". If I imagine future touchscreens I am sure they would "zoom in"/"make text bigger" by making a two finger motion where you move the fingers away from eachother (I think this is already done somewhere, it rings a bell), which again equals mousewheeldown for me.

'"Up" equals "more"' sounds very very wrong to me when we are looking at something text-based like websites. "more" is further down.

Complicated stuff, I wonder how much this is influenced by "math brains" and understanding of the technology/programming/something.

Cheers, Hannes


Well, you should be familiar with that from sliders. E.g. for volume - moving it up makes it louder. Or rating controls on social bookmarking sites. It's like this everywhere. So, even if it wouldn't make any sense whatsoever, it would be still "intuitive" to the user.

That two finger zoom gesture for touch screens... well, that's about manipulating the viewport, which means that there are other rules in effect. (Same goes for scrolling by the way.)

Pulling down... interesting. However, the fixation and the grabbed point are arbitrary. If they are switched "up" would equal "bigger" again.

Well, do what I did. Ask some casual PC users to increase the font size via ctrl+mhweel and observe what they are actually doing. (If only geeks are available ask 'em first if they've ever changed the font size via ctrl+mwheel before doing the test.)


Firefox you are a GOD SEND. Tomorrow,April 6th. is my birthday. I will be 94. Now thanks to you I can see text again. I will never forget you.

re: Firefox

Happy birthday Randy! :)

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