26 Firefox Quantum 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 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. These are Make Tech Easier's favorite Firefox about:config tricks, freshly updated for Firefox Quantum.

Also read: 7 Best Firefox Extensions You Need to Use in 2021

How to Access "about:config"

Type about:config into Firefox's 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.

Firefox About Config Tips Accept The Risk

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 this 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.

Note: to undo specific changes you make in about:config, just right-click the entry you want to revert and click "Reset."

You'll have plenty of programs and apps on your PC that link to your browser – whether linking to your email provider, an online manual for a program, whatever. By default, Firefox will open links from other apps as a new tab, but you can change this to instead be a new window or to force itself into an existing open tab.

Firefox About Config Tips New Window Override

To change this, go to browser.link.open_newwindow in Firefox, then next to browser.link.open_newwindow.override.external, change the number to one of the following:

  • 1: Force new window into existing open tab
  • 2: Open a new window
  • 3: Open link in a new tab

2. Change Number of Content Processes

Do you like to work with a lot of tabs open at any one time, or do you rarely have more than, say, five tabs open? The more content processes you have, the more CPU resources will be assigned to each tab (which will also use more RAM).

If you have a powerful PC, then you can set this at a reasonably high number, which should improve the stability and performance of each open tab in Firefox. The name of this setting in about:config is dom.ipc.processCount.

Default value: 8

Modified value: 7-12 (depending on number of tabs you usually have open)

3. Disable Unnecessary Animations

Animations in Firefox Quantum are not a bad thing, but if you have an old PC where every MB of RAM counts or simply don't need these animated flourishes, you can disable them by going to toolkit.cosmeticAnimations.enabled and setting the value to "false."

Default value: true
Modified value: false

4. Change Minimum Tab Width

It will take a more sharp-eyed Firefox user to notice this adjustment Mozilla made to Firefox Quantum. The default tab width is now just 76 pixels, whereas before it was 100. To adjust this, go to browser.tabs.tabMinWidth.

Default value: 76
Modified value: 100 if you want the same tab width as in older versions of Firefox, but really you can make this whatever you like. Just don't go overboard!

5. Reduce Session History Cache, Save RAM

If you're using an older machine, then even the typically speedy Firefox may slow down your PC with the default settings. This could be in part because of how it stores Web pages in its short-term memory (or RAM), which you can access using the Back and Forward buttons.

Firefox About Config Tips Session History

The preference browser.sessionhistory.max_total_viewers affects how many pages Firefox stores in such a way that they load super fast.

Default value: - 1 (adaptable)
Modified value: any number, reflecting the number of pages you want to store. (We recommend less than 4 if your PC is struggling for speed, while those with 4GB plus can go for 8 or more.)

The preference browser.sessionhistory.max_entries affects how many pages each tab stores in its Back/Forward history altogether.

Default value: 50
Modified value: If your PC is struggling, lower this to 25, check if it helps, then adjust accordingly.

Also read: How to Easily Save Every Images On A Web Page In Firefox

6. Disable Extension Compatibility Checks

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."
Firefox About Config Tips Compatibility Checks

7. Change Firefox Download Location

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

8. Get Asked Where You Want Each Download Saved

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

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

Firefox About Config Tips Download Direct

Note: this option is also available in its Preferences section. Go to "Preferences -> General -> Downloads" and select "Always ask you where to save files."

9. Open New Tab for Search Box Results

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

10. Adjust the Smart Location Bar's Number of Suggestions

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.

11. Adjust the Session Restore Saving Frequency

Firefox saves your session every 15 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 second, and 60000 means one minute.

12. Extend Scripts' Execution Time

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 may 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

13. Handling JavaScript Popups

When you come across a site that executes a javascript, open a new window function, and if the pop-up window is without all the usual window features, e.g. back/forward/reload buttons, status bar, etc., Firefox will automatically treat it as a pop-up 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

14. Enable Spell-Checking in All Text Fields

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 (spellcheck for multi-line text boxes only)
Modified values:

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

15. Lower Memory Usage When Minimized

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 value: True.

16. Increase/Decrease the Amount of Disk Cache

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: 256000 (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

17. Select All Text When You Click on the URL Bar

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 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

Also read: How to Reduce Firefox Memory Usage

18. Same Zoom Level for Every Site

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)

19. Setting Your Zoom Limit

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: 500 (percent)
Modified value: any value higher than 300

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

20. Configure Your Backspace Button

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

21. Increase Offline Cache

If you do not have access to the Internet most of the time, you may 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

22. Disable Delay Time When Installing Add-ons

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)

23. View Source in Your Favorite Editor

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)

25. Autohide Toolbar in Fullscreen Mode

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)

26. Increase Add-on Search Result

If you go to "Tools -> Add-ons -> Get Add-ons" and perform a search, Firefox will display 15 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. For more Firefox tips, see our guide on how to reduce memory usage in Firefox and how to find and replace text in Chrome and Firefox.

Robert Zak

Tech writer at Make Tech Easier. Enjoys Android, Windows, and tinkering with retro console emulation to breaking point.

Subscribe to our newsletter!

Our latest tutorials delivered straight to your inbox