Nglayout.debug.checksum xul fastload file

From MozillaZine Knowledge Base



To improve performance, Mozilla saves a “compiled” version of the XUL and JavaScript to disk periodically so that it does not have to re-parse the data from chrome files on startup. This caching (often referred to as “XUL FastLoad” or just “FastLoad”) significantly decreases the time it takes to do a cold start of a Mozilla application.

By calculating a checksum of the FastLoad file and comparing it to past checksums, Mozilla can verify that the file hasn’t been subject to corruption or modification by an outside source. This preference determines whether Mozilla calculates a checksum on the file.

Possible values and their effects


Calculate the checksum of the FastLoad file to verify that it hasn’t change since the last time the file was written to disk. (Default)


Do not verify the FastLoad file’s checksum.

First checked in

2001-07-31 by Brendan Eich

Has an effect in

  • Mozilla Suite (all versions since 0.9.4)
  • Mozilla Firefox (all versions)
  • Mozilla Thunderbird (all versions)
  • SeaMonkey (all versions)

Related bugs

Related preferences