Fix for scrollbar in Firefox 4.0 not working with Synaptics touchpad

Question

Since updating to Firefox 4.0 I'm having trouble scrolling with the touchpad on my Dell laptop. I followed all the instructions here: http://support.mozilla.com/en-US/kb/Cannot%20scroll%20with%20mouse%20wheel%20or%20touchpad - updated the driver, then changing the settings in Firefox.
After changing both the .numlines and .sysnumlines settings and restarting Firefox, the scrollbar works once or twice, then stops. If I change the settings and restart Firefox, I can get it to work again, but really - that gets old fast. Is there something that would be a more permanent fix?

Answer 1

Its due to the adobe reader add on. I removed adobe reader and installed foxit reader. Now everything seems perfect. My laptop model is model is Acer Aspire 5820 TG and I use synaptics driver.
Solution: (Courtesy - iuliand)
If you have issues with touch-pad scrolling in FF4 do this:
1) disable Adobe Acrobat add-on and test if it works, otherwise
2) install the latest touch-pad driver.
Hope this will help others.
Edit:
If the above does not work, temporarily disable all add-ons in order to check if there is another one that may cause this.
Also, make sure you update to the latest touch-pad driver from the touch-pad manufacturer site (very easy to do if you have a Synaptics). Most of the time drivers from notebook manufacturer support site are NOT up to date.
Keep in mind that you may need to do both things (disable acrobat AND install latest driver). Both are possible causes and may occur at the same time, as it was in my case.
Edit 2:
If you have an ALPS touch-pad and none of the above works, check dog425's post below in this topic. He pointed out a solution found in this thread: https://support.mozilla.com/en-US/questions/791829#answer-163071