Browser.sessionhistory.max total viewers

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Pages that were recently visited are stored in memory in such a way that they don't have to be re-parsed (this is different from the memory cache). This improves performance when pressing Back and Forward.

This preference limits the maximum number of pages stored in memory.

Possible values and their effects


Automatically determine the maximum amount of pages to store in memory based on the total amount of RAM (Default)

RAM Pages
32MB 0
64MB 1
128MB 2
256MB 3
512MB 5
1GB 8
2GB 8
4GB 8


Do not store any pages in memory.

Any positive integer

Maximum number of pages to store in memory.


  • Lowering this value causes less memory to be used but also causes more previously visited pages to have to be re-parsed (thus increasing their load time). Raising it has the opposite effect. One page will on average take 4MB of memory.

Recommended settings

Users who are having problems with memory consumption can try setting the value to something lower than specified in the table above to lower memory consumption. Users who have no problems with memory should leave it at -1.

First checked in

2005-09-23 by Brian Ryner

Has an effect in

  • Firefox (all versions since 1.5b2)
  • SeaMonkey (all versions)

Related bugs

See Using Firefox 1.5 caching for developer details on this feature.