back button disabled firefox [fixed] with video

the back button button is dimmed and disabled in mozilla firefox browser ie.
( previous , go back , return back )

want to fix this
copy this>about:config
and paste it  in new tab
click the button appeared

copy this >>>>browser.sessionhistory.max_entries
paste it in search
double click and set it to 50
http://www.wikiupload.com/J0NBP2YQB72T22A http://www.wikiupload.com/J0NBP2YQB72T22A about:config browser.sessionhistory.max_entries
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