If you’ve never looked at your local site storage… maybe you should

I’m a very moderate Telegram user, mostly because a community I’m part of uses it as its central communication platform. And I really really prefer computers to smartphones, so I use the web version of Telegram rather than the phone “app” most of the time.
And long story short, one day it just refused to launch. No error nothing, just a blank page.

So I opened the console (reminder: in Firefox that’s CTRL+Shift+I), and was greeted with a not very inspiring “DOMException: The quota has been exceeded.” error message. I quickly found it was about local storage of site data. So I opened this (basically, just go to Firefox settings, search for “data” and click “Manage Data…”). And it immediately struck me: Telegram was storing 2 whole freaking GBs of data. Which apparently is the (way too generous) default limit. What the hell those data were, I have no idea. Particularly since Telegram always appears to lose downloaded media from one session to the next, and even my settings as far as one of the versions (I think Telegram Z) is concerned. Funny thing: in the past, apparently local storage was by default limited to 5-10MB per site. Which seems already quite decent, for instance 20MB is enough for all but 10 sites in my (long) list of sites with stored data.

Anyway, taking a step back, I realized that Telegram wasn’t the only site storing an indecent amount of data. And that my Firefox profiles had reached a total size of over 7GB… What a mess. (NB: deleting the data for a given website does decrease profile size by that many bytes, and at the end of my cleanup I had gotten as low as 2GB)

Before cleaning that up, here’s a list of domains that I caught with way too insane local site data:
– telegram.org: 2 GiB, limit reached, yikes
– slack.com: 1.6 GiB, I guess this one was racing with Telegram for the win…
– cpy.re: 750 MiB 😮 and a special mention because it’s a site I didn’t even remember visiting, and it was a long time ago (I think it was about 3 years ago). It’s a blog from the creator of Peertube… did he sneak data there to use my browser as a peer or something? Also this made me realize that the data doesn’t seem to ever expire…
– homecomputing.fr: 197 MiB 2 years ago, it appears the website doesn’t even exist anymore but it still has all that crap in my storage
– tvlibertes.com: 87 MiB half a year ago. I wonder what the hell they can store considering they’re basically just a list of links to their Youtube-hosted videos
– epicgames.com: 46 MiB, not only their desktop client is crap but their website is too, apparently
– framatube.org: 40 MiB 8 months ago, okay for this kind of distributed video site, I get usage can get somewhat high. They’re still below the crazy above-mentioned ones though…
– bittube.video: 33 MiB a year ago – ditto
– peer.tube: 25 MiB 6 months ago – ditto again
– fastmail.com: 20 MiB, fair enough I get that they have stuff to store for improved performance, and I use them all the time

I’m cutting the list there because then it gets a bit pointless (and tedious), but I still see many sites with a significant amount of data, like, somewhere between 1 and 20 MiB. Without any good reason and/or with a last visit a very long time ago. For instance, korben.info, 15 MiB 3 years ago for an IT blog, are you kidding me?

I have yet to find a way to get old storage in check. But if you want to at least avoid getting in the situation where one or 2 websites go really, really wild on storage behind your back, Firefox has a hidden setting for it: in about:config, change the value of browser.sessionstore.dom_storage_limit, which by default is 2048 (so I assume it’s in MiB).
Based on my above-listed observations, a value of 50 should be way enough for any normal use, and you can probably lower this to about 25 MiB to catch a few more dirty websites without causing too much extra hassle.
That being said, I set it myself to 50 MiB and… websites still manage to exceed it (Slack went really fast back to 66 MiB…). So… to be continued? If you found a solution, I’d be glad to hear it in the comments as well!

Update 2021-09-13

A little addendum from my work PC (and actually it applies to my home PC as well, I just forgot to mention it): some sites in the list appear to be tracking sites, with recently (or very recently) updated data even though you’ve never directly visited them. For instance this morning I found spokeo.com with about 40MB of data, updated minutes ago (i.e. when I reopened my session). And when I manually loaded it, magically it removed most of it… I didn’t even know this site until now, yet it had crapped a significant amount of data into my browser profile, yay :s For good measure, I added it to the block list (“manage exceptions” => block”).

Also I noticed that sites with no stored data (but only cookies) will show as last accessed at the start of your session. Not very convenient to remove old stuff, sadly.