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Firefox saves user preferences to prefs.js when exit it, is this redundant?

  • 3 replies
  • 1 has this problem
  • 10 views
  • Last reply by cor-el

jindongpu
jindongpu
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I have a question regarding to why Firefox saves user preferences to prefs.js when exit it.

My observation is that Firefox saves changes immediately to prefs.js when users modify preferences either through Option (Windows)/Preferences (Mac, Linux) menu or directly through about:config page. Therefore, the prefs.js file should always in sync with the browser.

However, I notice that Firefox saves preferences to prefs.js in the end when I exit the browser. I am wondering if this feature is redundant since all preferences are in sync between prefs.js and browser? Or maybe some preferences are not saved immediately? If that is the case, how to identify those preferences that are not saved immediately?

Thanks in advance!

I have a question regarding to why Firefox saves user preferences to prefs.js when exit it. My observation is that Firefox saves changes immediately to prefs.js when users modify preferences either through Option (Windows)/Preferences (Mac, Linux) menu or directly through about:config page. Therefore, the prefs.js file should always in sync with the browser. However, I notice that Firefox saves preferences to prefs.js in the end when I exit the browser. I am wondering if this feature is redundant since all preferences are in sync between prefs.js and browser? Or maybe some preferences are not saved immediately? If that is the case, how to identify those preferences that are not saved immediately? Thanks in advance!

All Replies (3)

cor-el
cor-el
  • Moderator
  • Top 10 Contributor
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You can make a copy of prefs.js before closing and compare the two files.

jindongpu
jindongpu Question owner
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Hi cor-el,

Thanks for your replay! I tried the method you suggested. First, I open Firefox and make a copy of prefs.js, namely, prefs.js.old. Then I exit firefox and "diff" prefs.js and prefs.js.old. It turns out that the two files are identical. It looks like writing to prefs.js when exiting Firefox seems not necessary, because prefs.js is always in sync with the browser. Do you know what is the purpose of writing to prefs.js when exiting Firefox? Thanks!

cor-el
cor-el
  • Moderator
  • Top 10 Contributor
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It is possible that there are situations where there are some prefs that need to be changed and where the two files differ.
This can happen if you use Clear Recent History and Firefox wasn't able to complete that task.
Another possibility is to restart Firefox to complete the installation of add-ons and there are probably more cases.