If you read long texts with a web browser, it is easier for the eye to have something that guides them.

One simple solution is to read at the bottom of the screen and scroll down one line after the other.

Up to now I could not find a way to scroll exactly *one** line with Firefox. Cursor-Down moves more than one line in my setup.

A plugin which provides a ruler or something like this would work, too.

If another browser supports this I am willing to change.

Has someone got a solution?

  • Just saying, exactly one line on all websites won't be possible, because they can have different font-sizes and line-heights. You'll have to adjust it on every site manually once you find out how. Aug 18, 2015 at 15:28
  • @PeterNerlich yes your are right. Most sites use a lot of fonts. But there is one that gets used the most.
    – guettli
    Aug 19, 2015 at 11:00

6 Answers 6


As mentioned in this Mozilla support page, You could try changing one (or both) of these hidden settings:

(1) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.

(2) In the search box above the list, type or paste wheel and pause while the list is filtered

(3A) Double-click the mousewheel.default.delta_multiplier_y preference and type in a higher value to make each movement of the wheel cover more ground. For example, you could try 300 or 500. You can keep this tab open and experiment with scrolling in a different tab until you find a value that gives you the speed you're looking for.

(3B) Double-click the mousewheel.system_scroll_override_on_root_content.vertical.factor preference and type in a higher value. For example, try changing 200 to 500. You can keep this tab open and experiment with scrolling in a different tab until you find a value that gives you the speed you're looking for.

  • Changing values from 300 to 500 won't help here. I want this to work for every font size. I won't change the about:config values for every page I want to read line by line.
    – guettli
    Aug 14, 2015 at 19:03
  • @guettli changing the multiplier to a lower value will simply slow down your wheel so it can cover less space. And it's global for all of Firefox. Aug 14, 2015 at 19:18

This answer was originally written for Firefox Legacy. The alternative add-ons for Firefox Quantum may be found in other answers.

The easiest way is probably to use the extension: SmoothWheel

The extension is no longer found on Mozilla Add-ons site but still available via home page at mozdev.org, which likely for Firefox 56 or older version only. This extension gives extended options to customize your scrolling experience, by controlling the step size and speed of scrolling. Have a look at screenshot below.

SmoothWheel, an extension for Firefox Legacy

The default setting is somewhat smoother than before installing the Add-ons, but likely too fast for what you want. Try the following suggestion (tried by myself).

Scroll settings

Under Basic - Scroll, change accordingly:

  • Step Size: 1/5 page --> 5 pixels

  • Speed: Normal (0.4 sec) --> Relaxed (0.7 sec)

Then, click Apply button to make changes effective. At this point, you may notice that the page "accelerates" depending on your scrolling gesture habit. For more consistent feel, continue with following steps.

Under Advanced - Advanced Scroll Settings, change accordingly:

  • Adaptive-Duration: Medium (x2.5) --> [DISABLED]

Finally, click Apply button again. Now you will notice that the scrolling is more "even" and consistent at each steps.

Scroll experience

If you experience occasional short hangs, you might want to visit this page that explains about VSync and other issues.

Up to now I could not find a way to scroll exactly one line with firefox.

While this solution may not give you exactly one line in Firefox, 5 pixels is the smallest step (followed by 1/20 page) you could get with this Add-ons. And perhaps less risky than tweaking in about:config.

From my testing experience scrolling on this Mozilla Contribute page (2015), 1/20 page feels like something between 20 pixels and 50 pixels. That being said, 1/20 page might scroll more or less, depending on page contents and font size.

  • 1
    I guess (have not tried it yet) that scrolling 1/20 of a page does depend on the font size. On some font sizes you can scroll one line, but if the font is bigger or smaller, it won't work. But up to now this is only a guess. I need to try it first
    – guettli
    Aug 17, 2015 at 5:52
  • @guettli Updated my answer; I missed the 5 pixels option because it is found in the middle of list. The N-pixels option should be more accurate regardless of font size.
    – user37165
    Aug 18, 2015 at 15:24

You can use Yet Another Smooth Scrolling extension for Firefox:


Then it is pretty easy to customize scroll options for both keyboard and mousewheel.

Go to the extensions' preferences and choose a stepsize of keyboard or mouse depending on the font of your browser. (For me 22 worked well, with my font Georgia,size 15).

enter image description here


Go to Preferences and then under the Advanced sub-menu uncheck Use smooth scrolling.

enter image description here

This should let you scroll more precisely, you just need to scroll very slowly.

  • smooth scrolling is already activated in my settings. Sorry, at least in my browser (Firefox 37.0.2) this option does not help. Unchecking it had no effect. At least when scrolling in wikipedia pages.
    – guettli
    Jun 7, 2015 at 19:37
  • I'm using Firefox 38.0.5 and disabling smooth scrolling lets me scroll one line at time.
    – user404182
    Jun 7, 2015 at 19:40
  • Just tried on Wikipedia, it scrolls two lines at time. Sorry, I don't know how to help you.
    – user404182
    Jun 7, 2015 at 19:41

Reading @PeterNerlich comment, I decided to make an extension to detect the font size and scroll by that number of pixels. I primarily use chrome and made the extension for chrome.

You may download the beta version from this link.

I've tested it in Windows version of chrome and Chromium Browser in Ubuntu 14.4.3. To include the gap between lines, I've multiplied the font size by 1.5. But, I'll provide a way to reduce or increase the gap factor in the next version. You may access Chrome Console(Ctrl+Shift+J ) to see the font size and read scroll data.

To install the extension, go to chrome://extensions/, drag and drop the beta file into the window. After that press the Add button.

Working of the extension:

  • See this IMAGE
  • Browse to the web page and press the extension icon.
  • Press "Detect Font Size!" button.
  • Immediately after you press the button, click on the text you wish to scroll line by line.

The window will now scroll according to the font-size.

I've also implemented code to bind the up and down keys in the keyboard just like the mouse wheel. I'll improve the functionality and release the next version shortly.


Uncheck Always use cursor keys to navigate within pages. This should permit a slower scroll via up and down arrows.

...except that scrolling within FF options pages seems a bit flaky, and possibly dependent on the size of character set in use.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.