nsISHistoryListener in Firefox 1.5

 called to notify a listener when the user presses the 'back' button
 of the browser OR when the user attempts to go back one page
 in history thro' other means, from javascript or using nsIWebNavigation

 @param aBackURI        The uri of the previous page  which is to be 
                        loaded.
 
 @return aReturn        A boolean flag returned by the listener to
                        indicate if the back operation is to be aborted 
                        or continued.  If the listener returns 'true', it indicates 
                        that the back operation can be continued. If the listener
                        returns 'false', then the back operation will be aborted.
                        This is a mechanism for the listener to control user's 
                        operations with history.
 

 called to notify a listener when the user presses the 'forward' button
 of the browser OR when the user attempts to go forward one page
 in history thro' other means, from javascript or using nsIWebNavigation

 @param aForwardURI     The uri of the next page  which is to be 
                        loaded.
 
 @return aReturn        A boolean flag returned by the listener to
                        indicate if the forward operation is to be aborted 
                        or continued.  If the listener returns 'true', it indicates 
                        that the forward operation can be continued. If the listener
                        returns 'false', then the forward operation will be aborted.
                        This is a mechanism for the listener to control user's 
                        operations with history.
 

 called to notify a listener when the user visits a page using the 'Go' menu
 of the browser OR when the user attempts to go to a page at a particular index
 through other means, like from javascript or using nsIWebNavigation

 @param aIndex        The index in history of the document to be loaded.
 @param aGotoURI      The uri of the document to be loaded.
 
 @return aReturn      A boolean flag  returned by the listener to
                      indicate if the GotoIndex operation is to be aborted 
                      or continued.  If the listener returns 'true', it indicates 
                      that the GotoIndex operation can be continued. If the listener
                      returns 'false', then the GotoIndex operation will be aborted.
                      This is a mechanism for the listener to control user's 
                      operations with history.
 

 called to notify a listener when a new document is
 added to session history. New documents are added to 
 session history by docshell when new pages are loaded
 in a frame or content area. 

 @param aNewURI     The uri of the document to be added to session history

 @return            <CODE>NS_OK</CODE> notification sent out successfully

 called to notify a listener when documents are removed from session
 history. Documents can be removed from session history for various 
 reasons. For example to control the memory usage of the browser, to 
 prevent users from loading documents from history, to erase evidence of
 prior page loads etc... To purge documents from session history call
 nsISHistory::PurgeHistory()

 @param aNumEntries   The number of documents to be removed from session history.
 
 @return aReturn      A boolean flag returned by the listener to
                      indicate if the purge operation is to be aborted 
                      or continued.  If the listener returns 'true', it indicates 
                      that the purge operation can be continued. If the listener
                      returns 'false', then the purge operation will be aborted.
                      This is a mechanism for the listener to control user's 
                      operations with history.

 @note                While purging history, the older documents are removed
                      and newly loaded documents are kept. For example  if there
                      are 5 documents in history, and nsISHistory::PurgeHistory(3)
                      is called, then, document 1, 2 and 3 are removed from history
                      and most recently loaded document 4 and 5 are kept.
 

 
 called to notify a listener when the user presses the 'reload' button
 of the browser OR when the user attempts to reload the current document
 through other means, like from javascript or using nsIWebNavigation

 @param aReloadURI    The uri of the current document  to be reloaded.
 @param aReloadFlags  Flags that indicate how the document is to be 
                      refreshed. For example, from cache or bypassing
                      cache and/or Proxy server. 
 @return aReturn      A boolean flag returned by the listener to indicate 
                      if the reload operation is to be aborted or continued.
                      If the listener returns 'true', it indicates that the 
                      reload operation can be continued. If the listener
                      returns 'false', then the reload operation will be aborted.
                      This is a mechanism for the listener to control user's 
                      operations with history.
 @see  nsIWebNavigation