# firefoxtweaks: profile on ramdisk is the only way to stop its constant disk io

i have a raspberry pi 4 on which i'm using firefox. raspberries use sdcards as their disk. sdcards are known to have limited lifespans. and when i look at firefox's disk activity, i see that it's constantly writing to disk. it does it even when i'm doing nothing in the browser. programs doing constant busywork are bothering me. and it is doubly bothering me when they are wearing down my hardware.

anyway, in this post i document my adventures in configuring firefox on linux in case i ever need to recreate this on other machines.

# measuring disk i/o

there are many ways to measure disk i/o but i went for a very simple way. i wrote a small go script that recursively installs inotify watches in every directory in my home directory: @/listwrites.go. those inotify watches report every file write event. it's not perfect as i don't think it detects mmap writes but it's good enough for me.

i've seen a lot of activity in the profiles directory. i've learned that firefox keeps lot of its data in sqlite files and it is constantly editing those. thanks to the file names i managed to find a few tweaks that reduced the activity levels.

# io tweaks

all these tweaks should be done in either about:config or in a file called user.js in the profile's directory. i edit user.js because then i can put it into my dotfiles repo and share it across installations. i'll post my changes as what one would enter into user.js. should be obvious how to make the change in about:config from that.

first, firefox aggressively caches web content. i don't see much point persisting its cache onto disk so i'll simply disable that:

  user_pref("browser.cache.disk.enable", false);

there's still some constant writing, i think for the ability to restore my tabs in case firefox crashes. i'm not sure i can disable this, but i can bump its interval:

  user_pref("browser.sessionstore.interval", 6000000);

with the above io tweaks i see reduced io but unfortunately it is not zero and i'm not sure what else to disable. this wouldn't even bother me too much if firefox would just write and then that be it. then i can simply bump the disk dirty page expiration times in the kernel settings and there won't be any disk io. but due to how sqlite works, the writes are fsync'd which forces a disk write regardless of the dirty page expiry settings.

# profile in tmpfs

since i couldn't figure out how to eliminate the rest of the writes, i decided to put my profile into a ramdisk. i simply point firefox to a profile in /dev/shm. i sync the contents to the on-disk backup every 4 hours via rsync.

i implement this via a wrapper script i wrote in go: https://github.com/ypsu/cfg/blob/master/utils/firefox.go. i simply run "firefox" and it does it's magic. it does nothing on machines where i have not set this up.

it needs some setup in .mozilla/firefox though. append ".disk" to the default profile's directory name. then create a symlink to the target tmpfs directory as the profile name. firefox will be none the wiser that the profile is in tmpfs.

there are more advanced solutions to this: https://wiki.archlinux.org/title/profile-sync-daemon. it has much more features. i'm using my own short script so that i don't need to install gazillion things whenever i move to a different machine. and i don't like running daemons anyway.

# other configuration

there are other minor annoyances like caret blinking. i often use an e-ink screen (see @/dasung) and caret blinking is wearing down my screen! and as i established above, i hate software wearing down my devices. fortunately stuff like this is easy to disable in firefox:

  user_pref("ui.caretBlinkTime", 0);

i have bunch of other knobs for many random other things such as disabling search and autocompletion in the url bar, disabling warning screens, etc. all these settings are in my dotfiles repo: https://github.com/ypsu/cfg/blob/master/misc/firefoxuser.js.

i also customize my search engines. the installation script for those is also in my repo: https://github.com/ypsu/cfg/blob/master/misc/firefoxsetup.

i also install ublock origin as the adblocker because the internet is unusable without it. sometimes i also disable web workers via ublock origin. web workers allow the browser to run multiple background js threads with which it can consume even more resources, even mine bitcoins via all your cores. if you allow push notifications for a site, then the website's web worker can run even when the website is closed. dunno, it feels wrong that web workers are not permission gated. i block them by adding the following to the "my filters" config section:

  ||$csp=worker-src 'none',domain=~exampledomain.com

the exampledomain bit is for me a reminder how to allowlist specific websites where i would want the workers to work in the future without needing to fully disable ublock for that site. but in practice i'd just disable ublock for the site if i needed web workers e.g. for offline access.

# chrome

a sidenote about chrome. i hate chrome's approach to configuration. they try to hide most settings because they have some unreasonable fear of knobs. their android app doesn't even allow installing extensions. how would its parent company make money if people install adblock, right?

fortunately if you are willing to read the source code, you can often find some hidden command line switches for specific behavior. for example at work this is how i start chrome in order to disable the stupid autocompletion in the url bar:

  chrome \
    --enable-features="OmniboxUIExperimentMaxAutocompleteMatches:UIMaxAutocompleteMatches/1/UIMaxAutocompleteMatchesByProvider/*%3A0" \
    --disable-features="UrlScoringModel" \
    --force-prefers-reduced-motion \
    "$@"

sigh. and i'm not sure this hidden setting will stay around. as a precaution i check the presence of the flag at the head version every time i start the browser: https://github.com/ypsu/cfg/blob/master/utils/xchrome. if i notice that some developer removed my flag, i can nicely ask them to put it back. i only use chrome because that's pretty much unavoidable at work for reasons™.

# wishes

i wish these things like the no-writes or simpler configurability would be better supported in the browsers. but i don't think as a user there's a way to ask for these things. the only way i can imagine is to actually work in these developer teams and then care about this and constantly push for these settings.

i think the problem is that these browser are funded by big advertisement companies and so the roadmap caters to their desires, less to the ordinary users. i wish they would be @/shapeware funded by both the users and the website operators.

edit on 2024-02-10: tweaked the chrome flags to make it work again.

published on 2023-07-01, last modified on 2024-02-10

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