Author Topic: Firefox and disk cache - not using it, but why?  (Read 77 times)

Dariusz Piatkowski

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Firefox and disk cache - not using it, but why?
« on: February 28, 2026, 06:04:17 am »
Hmm...so I've got what seems like a weird situations: my trusty FF 45.9 seemingly stopped using disk cache at some point in time.

Seeing as I would rarely check this, I honestly have no idea when this might have happened.

I have FF configured to automatically control the size of the disk cache, but even if I manually overwrite and force a max value, the count always stays at 0 (zero).

Hmm...indeed, looking at the FF profile directory I only find this:

Quote
Directory of G:\HOME\MOZILLA.ORG\USERPROFILES\Mozilla\Firefox\Profiles\p5gjgk21.Testing

 2-27-26  9:11p         <DIR>      0 ----  Cache
 2-27-26 11:44p         <DIR>      0 ----  cache2
 2-27-26 12:15p         <DIR>      0 ----  OfflineCache
 2-27-26  9:11p             1    124 a---  _CACHE_CLEAN_
        4 file(s)           1 bytes used

where: 'cache2' is what used to have all the disk cache entries, and it is empty...

HOWEVER

'Cache' does seem to have some stuff stored in it, such as:

Quote
Directory of G:\HOME\MOZILLA.ORG\USERPROFILES\Mozilla\Firefox\Profiles\p5gjgk21.Testing\cache

 2-27-26  9:11p         <DIR>      0 ----  .
 2-27-26 11:50p         <DIR>    388 ----  ..
 2-27-26  9:11p         <DIR>      0 ----  0
 2-27-26  9:11p         <DIR>      0 ----  1
 2-27-26  9:11p         <DIR>      0 ----  2
 2-27-26  9:11p         <DIR>      0 ----  3
 2-27-26  9:11p         <DIR>      0 ----  4
 2-27-26  9:11p         <DIR>      0 ----  5
 2-27-26  9:11p         <DIR>      0 ----  6
 2-27-26  9:11p         <DIR>      0 ----  7
 2-27-26  9:11p         <DIR>      0 ----  8
 2-27-26  9:11p         <DIR>      0 ----  9
 2-27-26  9:11p         <DIR>      0 ----  A
 2-27-26  9:11p         <DIR>      0 ----  B
 2-27-26  9:11p         <DIR>      0 ----  C
 2-27-26  9:11p         <DIR>      0 ----  D
 2-27-26  9:11p         <DIR>      0 ----  E
 2-27-26  9:11p         <DIR>      0 ----  F
 2-27-26  9:11p     4,194,304      0 a---  _CACHE_001_
 2-27-26  9:11p     4,194,304      0 a---  _CACHE_002_
 2-27-26  9:11p     4,194,304      0 a---  _CACHE_003_
 2-27-26  9:11p           276      0 a---  _CACHE_MAP_
       22 file(s)  12,583,188 bytes used

The problem being though: I have never seen 'Cache' being used before, as in none of my periodic FF Profile backups have ever showed it, nor does my FF install appear to be using this in any particular way.

The about:cache page shows the "G:\HOME\MOZILLA.ORG\USERPROFILES\Mozilla\Firefox\Profiles\p5gjgk21.Testing\cache2" as the proper disk cache location.

Anyways, I played around with changing various settings, the sort of OFF/ON again thing, but nothing seems to make a difference.

I'm curious if anyone has seen this behaviour before?
« Last Edit: March 01, 2026, 10:29:07 pm by Dariusz Piatkowski »

Dave Yeo

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Re: Firefox and disck cache - not using it, but why?
« Reply #1 on: March 01, 2026, 12:09:57 am »
I seem to have the same behaviour here. With SM as well. Wonder if one of updates broke something.
One thing I do is keep the cache on my ram disk so as not to wear my SSD. On Firefox need to add the string preference browser.cache.disk.parent_directory and point it to where you want.
I'll keep an eye on the cache

Dariusz Piatkowski

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Re: Firefox and disck cache - not using it, but why?
« Reply #2 on: March 01, 2026, 04:22:24 am »
Dave!

I seem to have the same behaviour here. With SM as well. Wonder if one of updates broke something.
One thing I do is keep the cache on my ram disk so as not to wear my SSD. On Firefox need to add the string preference browser.cache.disk.parent_directory and point it to where you want.
I'll keep an eye on the cache

I did quite a bit of surfing for the answer, but seeing how old our FF is very few topics were relevant. Having said that, I went through the regular suspects, such as: combination of private session setups and the previous bugs that would force the disk cache to be disabled...alas, those were actually FF releases prior to ours.

As it happens I try to do an occasional FF profile backup, but seeing as I haven't been really consistent with this (given that I do a DAILY rsync copy) the last backups I had were from Feb-2024...but no-go there, meaning, nothing was to be found in the 'cache2' subdirectory. Keep in mind though that in order to minimize the backup size I typically would purge the cache first before I ran the backup...lol, great intent, but that approach messes with our troubleshooting today!

Anyways, I did play around with re-directing to my RAMDISK, no change there.

I am going to revert to the previous cache engine setting and see if that does have any impact.

Dave Yeo

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Re: Firefox and disk cache - not using it, but why?
« Reply #3 on: March 01, 2026, 11:08:26 pm »
Quite possible I broke something over the years with security fixes from tenfour, changes to compile under the newer GCC etc, as I never checked the cache. It does work to a degree, after shutting the browser down and restarting some pages load from cache, though not as many as do under newer SM on Linux. SM, FF and TB share the code.
I have no idea where the cache code resides and don't feel motivated to explore the issue as it is working well enough in this broadband era.