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Some must-have Firefox hidden settings

How to hide the “download finished” bubble

This is controlled by the setting (edit it via about:config): set it to false to disable the highly annoying “download finished” popup which sloooooowwwwly appears and then diiiiiiiiisappeeeaaaars every time a file has finished downloading (this thing is particularly slow when your GPU is busy doing something else).

How to skip antivirus scanning of incoming files + don’t tag downloaded exe’s as coming from Internet

This is controlled by the setting: set it to false to disable the bloody time-wasting virus scan at the end of every file download. This never caught a single virus for me anyway… Also, it makes the downloaded files bypass Windows security policy checks (the former preference was merged into this one), ie when you launch a downloaded executable Windows won’t bother you with the warning popup “this program was downloaded from Internet, are you sure you want to run it?”.

How to delete words from the personal dictionary

For some reason, I find it extremely easy to accidentally add misspelled words to the personal dictionary – I guess that menu item is somewhat misplaced. On the other hand, deleting them is then a pain in the ***, notably the GUI provides no way to do this. You’ll have to manually edit the dictionary file…
It’s located in your profile folder (on Windows NT/2k/XP/Vista/Se7en, it looks like %appdata%\Mozilla\Firefox\Profiles\xxxxxxxx.default – just browse to %appdata%\Mozilla\Firefox\Profiles\ then it will be obvious -, for other OSes, check out Profile folder on MozillaZine, or even simpler go to about:support and click on “Profile Directory – Open containing folder”) and is named persdict.dat. You can edit it with any plain text editor supporting Unix line breaks (for instance Notepad++ is good, the standard Windows notepad isn’t). Make sure that Firefox isn’t running, as it will overwrite the file when you close it. Source

How to configure several profiles

Close Firefox (make sure there’s really no more firefox.exe running in the background), then relaunch it with the -profilemanager argument. On Windows, the easiest way to do is is probably to hit [Windows key]+R (for “Run”), and then type firefox.exe -profilemanager. After that, you should get the profile manager window, which should be self-explanatory enough. If you need more details, this post should be helpful.
Edit: and if you want to run those separate profiles simultaneously, add the -no-remote flag.

How to prevent Firefox from trimming link URLs

That stupid feature was added when they replaced the status bar with that retarded add-on bar. Before that, when you hovered a link it’s target would show up in the status bar. As far as I remember, they then moved that preview to the address bar (with big fat huge trimming, as this is a limited and already well-filled space), and due to enough people getting upset with it, they moved it back to the bottom of the window (to the bottom-left, or when the find bar is opened (bug?), to the bottom-right), but this time above the add-on bar. BUT they didn’t remove the trimming: that URL preview is by default limited to 50% of the window’s width. Why the heck not 100%?? Anyway, to change that, go to your chrome folder (you might need to create it manually), which is located in %appdata%\Mozilla\Firefox\Profiles\xxxxxxxx.default\chrome (see the section about dictionary entries for more details and alternative OSes), then edit or create (with a plain text editor) the file userChrome.css. In this file, add the following section:
statuspanel {max-width: 100% !important;}
And voilà, when you restart Firefox link URL previews will be able to use the whole width of the window, so they shouldn’t get trimmed often, then…

How to decrease the minimum tab width

As in the previous tip, you need to create/edit userChrome.css. Add the following code (edit sizes as you wish):
.tabbrowser-tab[fadein]:not([pinned]) {
min-width: 15px !important;
max-width: 250px !important;}

How to force Firefox to display the full URL in the address bar

By this I mean, the real full URL, including the bloody http:// part. Well, I long thought this was impossible, but eventually a setting was created for this! In about:config, just set browser.urlbar.trimURLs to false. The change will be immediately visible! 🙂

How to hide all tab close buttons but the one on the active tab

I used to control this with the Tab Mix Plus extension, but clearly that’s overkill just to edit a simple setting… In about:config, just set browser.tabs.closeButtons to 0. The possible values are:
“0”: only show a close button on the currently selected browser tab
“1”: show a close button on all opened tabs
“2”: don’t show any tab-close button anywhere
“3”: only show a tab-close button at the end of the tab row

How to make Firefox Goolge-free

See How to eradicate Google from Firefox on Leave Google Behind. Long story short (just the steps, to make sure you don’t forget any):
1) Turn off “safe browsing”: this is the most sneaky one: with this “feature”, enabled by default, Firefox will send behind your back the URL of every site you visit to Google…
2) Disable geolocalisation: very sneaky too, this uses Google’s services to locate you (more specifically this URL:
3) Change your default search engine in the search bar (quite obvious)
4) Change the search engine in location bar search. Quite obvious too, Firefox can be a bitch with that: it will detected that the default search engine was modified, and at some point (like, a few days later) it will pop a big button (easy to click on accidentally) to put Google back there. Alternatively you can just disable location bar search (keyword.enabled = false)
5) Last but not least: change your homepage…

Well, that’s all for today… Those are pretty much all the dirty hacks I need to perform when dealing with a new Fx install, apart from the ever changing extensions.checkCompatibility mess. Keeping them on a single page should make my life easier the next time I need them…

Late updates

2017-10-07 – How to disable lazy loading

In their permanent race to try and match Big Brother Google’s Chrome speed, Firefox added lazy loading for tabs, enabled it by default, and didn’t think it would be wise to make it easy to disable this horrible shit. I guess it’s nice on a really slow computer, but on a fast one it just means you’ll waste time every time you switch to a not-yet-displayed-during-this-session tab. Still it can be disabled in about:config by setting those to false:
(hopefully they won’t change it again soon, the second setting was added after the first, which it broke, already :s)

2020-05-30 – How to get a warning whenever you close Fx

There’s been a mess that lasted years: with session restore becoming a thing, at some point the devs decided it didn’t make sense to warn the user when closing the browser. So they made the “warn on quit” option work only when session-restore was disabled. Which, in a way, made sense. But it also meant that the option wasn’t what it said on the can anymore. And it also left people looking to be warned when closing their session, no matter that they did have session restore on, without any option. And accidentally closing a 30 tabs sessions is always fucking annoying, even with session restore: at best it will take a good minute to be back in business, at worst you’ll lose form data and such.
Anyway, finally the option came back (it was a while ago already, I just never though of updating this post until now): just set browser.sessionstore.warnOnQuit to true.

Update on 2011-11-05

Firefox 94 fucked that setting yet once again for fucking fuck sake…
Now it’s browser.tabs.warnOnClose
Fuck Mozilla.

2020-05-30 – How to enable punycode

Long story short, hippies who like to create cool things without thinking about their security implications decided to allow to put many Unicode characters into domain names. The problem is, many Unicode characters look like your usual abcd letter while being actually a totally different character. Meaning you can create a domain name that looks just like, say,, without actually being Great for phishing. Not so good otherwise.
Gladly, browser vendors came with a counter-measure. Namely punycode, which converts Unicode characters back into ASCII, and then you really can’t miss it anymore because those converted characters look wild. But for some reason, the morons in charge at Firefox decided not to enable that feature by default… Unsecure by default, for a browser that keeps restricting user choices in the name of… security, if that’s not ironic I don’t know what is.
Anyway, to activate punycode, set network.IDN_show_punycode to true.

2021-05-03 – Don’t close Firefox when closing the last tab

I’m pretty sure there used to be a toggle for this in the options UI, but I guess they keep removing good stuff in an effort to become as crappy as Chrome…
Anyway, if you don’t want Firefox to close when you close the last tab (that’s notably quite useful for Tor Browser, because it’s so slow to open), in about:config set browser.tabs.closeWindowWithLastTab to false

2021-05-03 (again) – Disable “Default Browser Agent”

I recently switched back from ESR to normal Firefox (mainly because poorly made websites tend to perform like crap on even slightly outdated Firefox… thanks shitty front-end devs), and my firewall caught a new crapware in it: default-browser-agent.exe. From what I understood, it runs regularly, no matter if you open Firefox or not (seriously, freaking Mozilla?? The reason I don’t use Chrome is because I don’t want that kind of crap. Thanks!) and reports to Mozilla a bunch of info about your browser settings.

Supposedly, it shouldn’t activate if you turned telemetry off, but I do have telemetry off and still got it, so…
Setting default-browser-agent.enabled to false in about:config should do the trick, but you may want to also remove the “Firefox Default Browser Agent” task in Windows Task Scheduler, and set, in regedit, a DWORD value HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Mozilla\Firefox\DisableDefaultBrowserAgent to 1. For good measure, you may want to also delete default-browser-agent.exe and pingsender.exe from your Firefox installation folder. Although I’m quite positive it will come back at the first update (but deactivated… hopefully). Not intrusive at all, thanks for making it so simple to have a little privacy, Mozilla 😡

Update on 2023-02-28: There’s also a task to disable or delete in the Task Scheduler. That task’s description says that updating the above-mentioned preference is enough (obviously a lie) and also they mention adding a Firefox enterprise policy setting “DisableDefaultBrowserAgent” set to true in Firefox’s installation folder distribution/policies.json (also a lie). Oh, and the reason I mentioned these parameters they mentioned are a lie is that I just caught that shit trying to pass my firewall on my new computer again, despite having set both.

2021-06-05 – Unlock compact mode

In Firefox 89, Mozilla hid the compact mode (apparently at first they fully removed it, but people got pissed – obviously) because it is “fairly hard to discover, and we assume gets low engagement”. Which brings the question of what the hell telemetry is for, and also looks like a strange way to solve UX issue. “OK, that great feature isn’t visible enough in the UX, so let’s remove it instead of, I don’t know, make it more visible?”
Anyway, people who already had compact mode enabled get to keep it and don’t need to do anything (yet). For the others, you can make it visible again by going to about:config and setting to true. In case you never found it before, it will be available at the bottom of the “Customize Toolbar” window (which can be access by right-clicking in an empty area of the toolbar, or in the menu => More tools ==> Customize Toolbar)

2021-06-10 – Proxying localhost

I’m surprised I didn’t already mention this. A long time ago, Firefox had localhost and pre-populated as default values in the “No Proxy For” configuration field. And suddenly they removed them but kept it as hidden defaults that can’t be removed, unless going to about:config. To be able to proxy localhost, now you need to set network.proxy.allow_hijacking_localhost to true. If you need more details, cf there for instance.

Posted in Firefox.

2 Responses

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  1. David says

    To disable lazy loading in Firefox 47+:
    – open about:config
    – set browser.sessionstore.restore_on_demand to false

  2. David says

    Also, the -profilemanager argument can be replaced with just -p

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