Tablets as they are today require you to jump through hoops and accept odd issues and lip sync. The best advice I can give is to return products that don't perform as well as you expected.
Yes, I was able to get Flash and Firefox Beta to work OK but as you noted, there is some issue with lip sync.
Since I see this on almost all tablets in the Browser+Flash issue or area I can't say if the product is ready for all of us.
I am partially disable and recently my daughter bought me a Galaxy Tab 2 (GT P-5113) to watch my favorite videos while in bed. However, to our surprise this tablet does not include Adobe Flash or any of the popular codecs.
I read of an older version of Adobe Flash for the Android os 4.0. However, my tab's os is 4.1.2.
I tried the trial version of the Puffin browser (Google Play Store) which has Adobe Flash included. This browser plays Flash videos but not without a few issues. The audio was out of sync and the picture quality is not good. I ventured to purchase the pay version of Puffin but the reviews were very bad.
It is amazing how the Galaxy Tab 2 plays YouTube Flash videos but no other Flash videos. I hope someone can assist me in this matter.