How to Fix Youtube Stuttering in Firefox
Since Firefox version 2 a feature called the session restore function has been implemented. This feature saves the tabs you have open every 10 seconds. This can cause flash video such as youtube to jump and stutter.
Fix
- open Firefox and in the address bar type about:config
- Click I’ll be careful to open the Firefox settings
- In the filter box type browser.sessionstore.interval
- Change this from 10000(10 seconds) to 120000(2 minutes)
This will reduce the lag when Firefox saves your open tabs
Let me know if this helped you! Leave a comment.

I have tried your fix and it does not appear to make any improvement. Any other suggestions.