25 Cool Firefox About:Config Tricks You Need to Learn

“Here be dragons,” reads the ominous disclaimer when you type about:config into Firefox’s URL bar, warning you that tweaking things in this area is largely experimental and can cause instability to your browser.

Sounds exciting, right? And even though it sounds a little scary, the fact is that you will almost certainly be okay when you start playing around in this area and can actually use the features here to improve and speed up your browser. Here are our favorite Firefox about:config tricks here at Make Tech Easier.

In Firefox type about:config into the address bar.

You will be shown that dragon-themed warning page. Click the “I accept the risk!” button, and you’ll arrive on the about:config homepage.


You’ll see a long list of configuration entries. If you’re looking for a specific one, type its name into the “Search” bar above the list.

To toggle different features on and off, simply double-click their entries under the “Value” column to switch between “true” and “false.” In some cases the value field will have a number instead. In ths case change the number to the one that corresponds to what you want. (Don’t mess around with these numbers until you know what you’re doing!)

Now, let’s get tweaking.

When you press Ctrl + Tab in Firefox, it will toggle between the different tabs you have open in your browser. This brings up slick little thumbnails showing each page you have open. It looks good but can be resource-consuming on weaker PCs, so you can turn it off by changing browser.ctrlTab.previews

Default value: true

Modified value: false – automatically switches pages on Ctrl+Tab instead of showing you thumbnails.


Compatibility checks. Who needs ’em, right? Actually they’re pretty handy as a general reference of which extensions will work with your version of Firefox and which won’t, but Firefox doesn’t always get it right. If you want to see whether an extension that Firefox claims is incompatible may actually work, do the following:

  • Right-click anywhere on the about:config page, then click “New -> Boolean”
  • Type extensions.checkCompatibility into the box, click OK, then select “false” and click OK again
  • This preference will now exist in your list, and you can disable it at any time by right-clicking it and clicking “Reset.”.


By default, Firefox downloads go to the Windows “Downloads” folder, but you can change this by tweaking browser.download.folderList

Default value: 1
Modified values:

  • 0 – Saves all downloads to the desktop
  • 2 – Saves to the same location as the previous download

If you want to have more direct control over your downloads and decide what directory you want each one to be saved in, change preference browser.download.useDownloadDir to “false.”

Default value: true
Modified value: false – prompts you where to save each download


By default, the things you search for in the Firefox search box open in the current tab. To open in a new tab instead, you’ll need to modify browser.search.openintab.

Default value: false – opens search results in current tab
Modified value: true – opens search results in new tab

Firefox’s New Tabs page organizes all the sites you’ve bookmarked and are most likely to visit in a convenient grid. Best of all, you can tweak how big this grid is, so while it’s 3×3 thumbnails by default, you can change it thanks to the browser.newtabpage.rows and browser.newtabpage.columns preferences.

Default value: 3 in “rows,” 5 in “columns”
Modified values: Whatever number you like!


Firefox’s animations are all flashy, firey and foxy, but they can also be a burden on older PCs. Here are the two key animation preferences you’ll want to modify to speed up your browser:

  • browser.tabs.animate: Set to “false” to turn off
  • browser.fullscreen.animate: Set to “false” to turn off

In Firefox when you start typing in the location (or URL) bar, a drop-down list of suggested sites will be shown. If you want it to show more (or less) than ten suggestions, you can adjust the browser.urlbar.maxRichResults keys and get it to show the number you want.

Default value: 10
Modified value: Set to your desired number of suggestions. If you want to disable it altogether, set it to -1.

Firefox saves your session every fifteen seconds by default, but you can change the value of browser.sessionstore.interval so that Firefox will save the session at a longer interval.

Default: 15000 (in msecs, equivalent to fifteen seconds)
Modified value: Set it to your desired value. 1000 means one sec, and 60000 means one minute

In Firefox a script is only given ten seconds to respond, after which it will issue an unresponsive script warning. If you are stuck on a slow network connection, you might want to increase the script execution time via dom.max_script_run_time to cut down on the frequency of the no script warning.

Default value: 10 (in secs)
Modified value: 20, or any value greater than 10

When you come across a site that executes a javascript, open a new window function, and if the popup window is without all the usual window features, e.g. back/forward/reload buttons, status bar, etc., Firefox will automatically treat it as a popup and will not open it as a new tab. However, if you find this to be a nuisance and want to open all new windows in new tabs, you can specify it via the browser.link.open_newwindow.restriction setting.

Default value: 2 – Open all JavaScript windows the same way you have Firefox handle new windows unless the JavaScript call specifies how to display the window
Modified values:

  • 0 – open all links the way you have Firefox handle new windows
  • 1 – do not open any new windows
  • 2 – open all links the way you have Firefox handle new windows unless Javascript specifies how to display the window

The default spell-checking function only checks for multi-line text boxes. You can change the option in layout.spellcheckDefault to get it to spell-check for single line text boxes as well.

Default value: 1 (spell-check for multi-line text boxes only)
Modified values:

  • 0 – disable spell-check
  • 2 – enable spell-check for all text boxes


This tweak is mainly for Windows users. When you minimize Firefox, it will send Firefox to your virtual memory and free up your physical memory for other programs to use. Firefox will reduce its physical memory usage, when minimized, to approximately 10MB (give or take some), and when you maximize Firefox it will take back the memory that it needs.

The preference name does not exist and needs to be created.

Right-click on the background and select “New -> Boolean.”

Enter the name when prompted: config.trim_on_minimize

Enter the values: True

Several tweaks are required for this:

Config name: network.http.proxy.pipelining
Default value: False
Modified value: True

Config name: network.http.max-connections
Default value: 30
Modified value: 96

Config name: network.http.max-connections-per-server
Default value: 15
Modified value: 32

When a page is loaded, Firefox will cache it into the hard disk so that it doesn’t need to be downloaded again the next time it is loaded. The bigger the storage size you cater for Firefox, the more pages it can cache.

Before you increase the disk cache size, make sure that browser.cache.disk.enable is set to “True.”

Config name: browser.cache.disk.capacity
Default value: 50000 (in KB)
Modified value:

  • 0 – disable disk caching
  • Any value lower than 50000 reduces the disk cache
  • Any value higher than 50000 increases the disk cache

In Windows and Mac Firefox highlights all text when you click on the URL bar. In Linux it does not select all the text. Instead, it places the cursor at the insertion point. Regardless of which platform you are using, you can now tweak browser.urlbar.clickSelectsAll to either select all or place the cursor at the insertion point.

Modified value:

  • False – place cursor at the insertion point
  • True – select all text when you click

Firefox remembers your zoom preference for each site and sets it to your preferences whenever you load the page. If you want the zoom level to be consistent from site to site, you can toggle the value of browser.zoom.siteSpecific from “True” to “False.”

Default value: True
Modified value: False (enable same zoom preferences for every site)

If you find that the max/min zoom level is still not sufficient for your viewing, you can change the zoom limit to suit your viewing habits.

Config name: zoom.maxPercent
Default value: 300 (percent)
Modified value: any value higher than 300

Config name: zoom.minPercent
Default value: 30 (percent)
Modified value: any value

In Firefox you can set your backspace by getting it to either go back to the previous page or scroll up a page if it’s a scrolling site. Holding Shift as a modifier will go forward a page if the value is set to 0 and scroll down if the value is set to 1.

Config name: browser.backspace_action
Default value: 0 – goes back a page
Modified value: 1 – scrolls up a page


If you do not have access to the Internet most of the time, you might want to increase the offline cache so that you can continue to work offline. By default, Firefox caches 500MB of data from supported offline web apps. You can change that value to any amount you like.

Config name: browser.cache.offline.capacity
Default value: 512000 (in KB)
Modified value: any value higher than 512000 will increase the cache value

Every time you install a Firefox add-on, you will have to wait for several seconds before the actual installation starts. To cut down on this waiting time, you can turn the preference security.dialog_enable_delay off so that the installation will begin immediately

Default value: 1000 (in msec)
Modified value:

  • 0 – starts installation immediately
  • any other value (in msec)


This is very useful for developers who are always using the “view source” function. This tweak allows you to view the source code of a given website in an external editor.

There are two configurations that need to be made:

Config name: view_source.editor.external
Default value: False
Modified value: True (enable view source using external text editor)

Config name: view_source.editor.path
Default value: blank
Modified value: insert the file path to your editor here

When you right-click and select “Save Link As…,” the browser will request the content disposition header from the URL to determine the filename. If the URL does not deliver the header within one second, Firefox will issue a timeout value. This could happen very frequently in a slow network connection environment. To prevent this issue from happening frequently, you can increase the timeout value to reduce the possibility of a timeout by editing Browser.download.saveLinkAsFilenameTimeout

Default value: 4000 (4 seconds)
Modified value: any value higher than 1000 (value is in msec)

In fullscreen mode the toolbar is set to autohide and appear only when you hover over it with your mouse. If you want, you can choose to have it visible all the time instead by toggling the value of browser.fullscreen.autohide to “False” to always show the toolbar.

Default value: True (always autohide)
Modified value: False (always show the toolbar)

If you go to “Tools -> Add-ons -> Get Add-ons” and perform a search there, Firefox will display fifteen matching results. If you want more or less results here, you can adjust extensions.getAddons.maxResults.

Default value: 15
Modified value: more or less than 15

The Firefox about:config section provides a powerful way for users to fully customize the browser. The above list is definitely not the complete list. There are tons of tricks that you can do with it. If you have any tricks not listed here, please add them in the comments.

This article was first published in 2008 and was updated in Oct 2017.

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