With the Firefox Download Day almost over, there is likely to be a whole load of new Firefox users as of today.

Even if you are a regular Firefox user, you still may not know about the advanced configuration options. To get these options, type about:config into the Firefox address bar. Once you hit return, you get a warning because modifying these preferences can (in rare circumstances) cause strange behaviour.

Clicking "I'll be careful, I promise!" brings up a huge list of preferences, most of which aren't accessible from the normal Preferences dialog. As the list is so long, the best way to find things in it is to start typing the name of the preference into the "Filter" box at the top. Once you have found the one you want, double-clicking it allows you to change it. Here's a list of my top 12 hidden Firefox preferences. All of them work in Firefox 3, but only some work in Firefox 2.

1. browser.urlbar.clickSelectsAll

The default behaviour, true, means that when you click the address bar, it automaticall selects all. Changing this to false stops this, and just inserts the cursor where you clicked.

2. browser.tabs.closeButtons

By default, Firefox displays a close button on every tab. Setting this preference to 0 will only display a close button on the currently open tab. Setting it to 3 will move the close button to the far right end of the tab bar, and setting it to 2 will get rid of all close buttons.

3. browser.search.openintab

Double-clicking this will set it to true. This makes searches from the box in the top right open in a new tab rather than the current one.

4. browser.urlbar.maxRichResults

Determines the maximum number of results that drop down from the URL bar when you start typing. Default is 12.

5. browser.fixup.alternate.suffix

Allows you to change the suffix that is automatically added when you don't specify one. For example you might want to change this to .co.uk so you will be directed here if you only type www.macosxtips.

6. browser.tabs.loadFolderAndReplace

If you open a whole folder of bookmarks at once using "Open All in Tabs", they replace all of your open tabs. Setting this preference to false will cause the new tabs to only replace the current tab and add in the rest after it.

7. accessibility.typeaheadfind.casesensitive

Setting to 1 Makes the Find function (Command-F) case sensitive.

8. ui.click_hold_context_menus

Set this to true to enable the click-and-hold way to open contextual menus.

9. browser.tabs.tabMinWidth

If you open lots of tabs in Firefox, they shrink down so they all fit across the screen. After a certain limit, your tabs don't get any smaller and you have to scroll to the left and right to view other tabs. This preference allows you to set the minimum width. Default is 100, lower values will give smaller tabs.

10. browser.chrome.toolbar_tips

Setting this to false disables the yellow tooltips that appear when you mouse over the bookmarks bar.

11. layout.spellcheckDefault

Changing this value to 2 makes the spell checker work in all text boxes, not just the large text fields.

12. browser.backspace_action

This changes the behaviour of the backspace key. setting it to 1 makes the backspace key scroll up a page in the current window. Shift-Backspace will scroll down. 2 to make the backspace key do nothing. Except delete when text is selected, of course. Changing to 0 will change back to the default behaviour of going back a page.


Of course there are hundreds more hidden settings in this list, including ones for extensions you have installed. If you know any more, add them in the comments.

Tootips are the little yellow boxes that appear when you hold your mouse over certain interface elements. For example, if you hold the cursor over a link in Safari, a tooltip will appear. In some cases this is useful, but often the yellow box will get in the way of other things.

Most of the time you can solve this by hitting return or enter. The tooltip should disappear. If you want to completely disable them, it is a little bit trickier. Annoyingly, tooltips are applications specific, so you have to enable/disable them in every application. Some applications have a preference to do this. Frustratingly, many do not.

Safari has a hidden preference to do this. To disable tooltips in Safari, open up the Terminal application (in the Applications/Utilities folder) and paste the following line:

defaults write com.apple.Safari WebKitShowsURLsInToolTips 0

Then press enter. You will need to quit and reload Safari for changes to take effect. Repeat with a 1 at the end instead of a 0 to reverse this. Note that tooltips are disabled by default in Safari 3. You can use this to enable them.

If you want to disable tooltips in Firefox, start by typing about:config into the address bar. In the list that appears, find browser.chrome.toolbar_tips. An easy way to find it is to start typing browser.chro into the filter box. Once you have found the item, double-click on it to change it from true to false. Now when you are browsing, tooltips should be disabled. Simply double-click again to change things back.

So you've just spent ages filling out all your details on a long web form, or have just written a 5000 work blog post. You are about to hit submit, but you notice a mistake. Going to correct it, you hit the delete key — but wait — the text field wasn't highlighted. You watch in horror as Firefox takes you back a page in your history, deleting everything you just wrote.

If that horror story sounds familiar, you might want to try changing the behaviour of the delete key in Firefox. Luckily, this is quite easy and doesn't require any Add-ons.


Start by opening up Firefox and typing about:config into the address bar. After you press return, you should see a huge list of Firefox preferences that you can change. Start typing browser.backspace into the filter box at the top, until you see the item called Browser.backspace_action. Double-click on it, and type one of the following:


Type 1 to make the backspace key scroll up a page in the current window. Shift-Backspace will scroll down. This is essentially the opposite hitting the space bar, which will scroll down a page and Shift-space will scroll up a page.

Type 2 to make the backspace key do nothing. Except delete when text is selected, of course.

Type 0 to change back to the default behaviour of going back a page. Note that Command-Left and Right also do this, as well as Command-[ and ].