If you cannot scroll up and down pages in Firefox using your mouse wheel or trackpad, it is either because you need to update your mouse/trackpad software (i.e. drivers) or because of incorrect Firefox settings.
In many cases, updating or re-installing the drivers for your mouse or touchpad will enable scrolling in Firefox.
An input driver is software that enables computer programs to interact with a hardware device.
Mouse drivers are often available for download from the mouse manufacturer's website. Visit the manufacturer website to find the drivers to download. For example, if you have a Logitech mouse, go to Logitech.com site and download the software associated with your mouse from its support section.
Touchpad drivers are often available from your laptop manufacturer's website. For example, if you have a Dell laptop, go to Dell Drivers and Downloads, specify your model, and download the software associated with your touchpad.
After downloading the drivers for your mouse or touchpad, install them and restart your computer. Even if the driver is not an update, re-installation will help if your computer is not using the driver.
You may also need to configure settings associated with the mouse. Examine the Keyboard & Mouse settings available in the System Preferences window for scroll-related settingsExamine the Mouse settings available in the Windows Control Panel for scroll-related settingsExamine your system's mouse preferences for scroll-related settings.
If updating or re-installing drivers did not work, you can try changing settings in Firefox:
In the address bar, type about:config and press EnterReturn.
The about:config "This might void your warranty!" warning page may appear. Click I'll be careful, I promise!I accept the risk! to continue to the about:config page.
In the Filter field, type mousewheel.withnokey.
Check these settings:
If mousewheel.withnokey.action does not have a value of 0, double-click on it and change it to 0.
If mousewheel.withnokey.numlines does not have a value of 1, double-click on it and change it to 1.
If you changed either of the previous two settings, test scrolling to see if it works. If it doesn't work, or if you didn't change either setting, double click mousewheel.withnokey.sysnumlines to change it from true to false (or vice-versa).