Sometimes the Linux Flash player starts lagging in the browser. This doesn't seem to fix it when trying to load Flash through another browser or restarting all browser windows completely.
A quick workaround in Chrome is playing with the Flash libraries. There is a version shipped together with Chrome and you can also use the library from the Flash player itself. If you have configured both .so files and navigate to:
Then you will find in the plugins list the Flash options similarly to the following screen:
By switching between the different libraries the lagging issue should get fixed. If not, update your library versions and use that approach when the browser rendering gets buggy again.