Many site issues can be caused by corrupt cookies or cache. In order to try to fix these problems, the first step is to clear both cookies and the cache. The Firefox cache temporarily stores images, scripts, and other parts of websites while you are browsing.
Note: This will temporarily log you out of all sites you're logged in to. To clear cache and cookies, do the following:

1. Tap the menu icon located at the top right corner. This is the icon with 3 bars. On older Android devices you'll have to press the hardware menu key and then tap More.
2. Tap Settings.
3. After that, you will be taken to the settings screen. In the settings screen, look under the section Privacy & Security and select Clear private data.
4. You will then be taken to a list of what can be cleared. Select the following 2 for deletion:
   • Cookies & active logins
   • Cache
5. After those have been selected, tap the Clear data button to actually clear the cache and cookies.

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even iam user of s3 used firefox 24 played video worked fine to fix you need to clearr cache or reinstall firefox some times cookie cashe gets corrupt

firefox tested on my s3 worked fine

Recent crashes of certain multimedia contents (this includes Youtube videos, certain flash games and other applications) in conjunction with Firefox are most probably caused by a recent Flash update and/or a malfunctioning browser plugin such as Real Player.

In order to remedy the problem, please perform the steps mentioned in these Knowledge Base articles:

• Flash Plugin - Keep it up to date and troubleshoot problems

• Adobe Flash plugin has crashed - Prevent it from happening again

• Flash 11.3 doesn't load video in Firefox

Other, more technical information about these issues can be found under these Links:

• http://forums.adobe.com/thread/1018071?tstart=0

• http://blogs.adobe.com/asset/2012/06/inside-flash-player-protected-mode-for-firefox.html

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