Thanks for that link. This helped fix the problem for me, I will explain what I did from that link that helped me..
My Background:
I have been having a similar problem as reported in this thread. I recently updated (an update installation not a clean install) to Yosemite from Maverick yesterday on Oct. 17, 2014. I have a 2013 Macbook Air.
My Problem:
When I was in Safari or Firefox, the two finger scroll worked fine initially. However, as soon as I tried to swipe right to go back to the previous page Safari and Firefox would stop responding to the scroll and swipe gestures on the trackpad and I would have to use the arrow keys to go up and down the page. The functionality would only temporarily return after I closed and reopened the programs.
I didn't take a screen shot before I found a fix to this problem but it looked like, on the left of the Safari browser, I could see a centimeter of another page behind the page I was viewing and this "double screen edge" would not go away even as I navigated to different pages and even though I only had one tab open.
What Fixed it for Me:
This is what I did that, so far, has fixed this problem. As I was able to replicate my problem previously and now that I can no longer replicate it, I consider this a "fix" for me. (All of my trackpad functionality has been working for the past couple of hours):
After I went to the page linked by boball:
https://forums.macrumors.com/threads/1681605/
I looked at the "alternative work-arounds" link that one of the posts referred to, which led me here:
http://www.bradycline.com/2012/in/stop-safari-reloading-on-back-gesture/
This page refers to resetting the preference options for "BetterTouchTool, MagicPrefs." I just use the default touch controls built into OS X, but I thought turning off all of the touch preferences and then turning them all back on might do something (plus it seemed like the least invasive method to try first.)
So I went into the trackpad settings in system preferences and I un-selected all of the options under "Point & Click," "Scroll & Zoom" and "More Gestures." I then closed the window and reopened it and reselected everything under those categories (I prefer to have them all selected for my computer use) and presto it seemed to have fixed the problem.
Post Script:
I hope this helps someone, I apologize for the long post but I thought if I was as clear as possible, in regards to what I did, it may be more helpful to everyone. Thanks to everyone who posted, you all helped me a great deal.