“Close Firefox – A copy of Firefox is already open. Only one copy of Firefox can be open at a time.”

You may have gotten this message if Firefox has recently crashed or you killed the process. The reason this error is appearing is likely because there is a lock file on your Firefox profile.

The easiest fix to resolve this “Close Firefox” error message is to remove the lock file from your profile, here is how to do this:

* Open the Terminal, you will need to navigate to your FireFox profile directory:
cd ~/Library/Application\ Support/Firefox/Profiles/
Now there will be a randomly generated name in here attached with a .default extension, like aioruajc.default or groeakc.default, once you’re in the Firefox Profiles directory you can find out what the randomly generated name is by typing:
ls
then type the cd command with whatever the random .default directory name is:
cd alaklrac.default
Once inside the .default Profiles directory, you can remove the lock file:
rm -rf .parentlock

You should now be able to relaunch Firefox without the error message.

Note: an alternate method to get to the proper Firefox Profiles directory is to type the following command:
cd ~/Library/Application\ Support/Firefox/Profiles/*.default
The * is a wildcard and will enter whatever directory ends with .default, this only works if you are using a single Firefox profile though. You can then remove the .parentlock file and relaunch Firefox as usual.

The web browsers most commonly used in Mac OS X are Safari and Firefox, here’s how to delete cookies in both.

Delete Cookies in Safari on Mac

* Open the ‘Safari’ menu in the upper left
* Click on ‘Preferences’
* Click the ‘Security’ tab with the lock icon
* Click ‘Show Cookies’ button
* Now click “Remove All” and ‘Done’
* Your cookies have been deleted in Safari!

Delete Cookies in Firefox on Mac

* Click on the ‘Firefox’ menu
* Navigate down to ‘Preferences’ and click
* Click on ‘Privacy’
* Click ‘Show Cookies’ or ‘Remove Individual Cookies’ button, depending on Firefox version
* Click ‘Remove All Cookies’
* Now your cookies are deleted in Firefox!

MouseOver popups, self-starting blasting audio, auto-refreshing webpages, random sound effects, obnoxious flash ads, resizing of your browser window… oh the web is filled with all sorts of things that are sure to annoy web browsers a world over. Lifehacker came up witha great list of fixes that you can implement in Firefox to reduce the most obnoxious encounters on the web (some work in Safari too). If your pop-up blocker isn’t doing enough for you, try these tricks out too:

Lifehacker: Use FireFox to Fix the Webs Biggest Annoyances

I like Safari but find myself in Firefox nearly always because of a multitude of reasons. One thing I’ve long missed though is the ability to view PDF’s within the browser within Firefox, which Safari does wonderfully. If you’re tired of Firefox launching the Preview app (or even worse if you’re settings are different: Acrobat), then try this great little Firefox extension, which will pop open the PDF file into a new browser tab. Note this requires Firefox 3

Firefox Mac PDF homepage
Download Firefox Mac PDF now

Life is officially easier for front-end web developers, you can now easily test browser compatibility by running Firefox 2 and Firefox 3 concurrently with a great utility called MultiFirefox. Simply install MultiFirefox, then rename one of the Firefox applications (to say, Firefox 3), and upon launch you can select either application version to run. MultiFirefox is fast, free, and simple to use, so check it out. Mac web developers rejoice!

Developer home
Download now

Here’s a really cool Firefox tip that was just passed along to me. You can instantly search for any text on a web page by hitting the forward slash and typing that word. So for example, you want to find “Firefox” on this page, you would type /firefox – that’s it! The first instance of “Firefox” will appear highlighted. This slash search feature is really just a shortcut to Command-F but it’s a lot faster if you ask me. This works across all platforms I have tried. Oh, and if you want to find the next instance of that word, hit Command-G (or Control-G if you’re in the Windows world). Check out more great Firefox tips.

Here’s a tip that I think you’ll appreciate as much as I do. By editing an entry within the about:config configuration menu of Firefox, you can enable spell checking in text input fields, meaning as you type into Google, your search term will be spell checked client-side! I type pretty fast so I frequently end up with typos, so this is a real life saver for me. Why isn’t this on by default? I don’t know, but here’s how to turn on Firefox text input field spell checking in three easy steps.

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I can’t count the number of times I have been closing windows or tabs and have accidentally a tab that I wanted kept open. In the past, it has been annoying at best and disastrous at worst, but now I no longer have any issues… why you may ask? Because I know a keyboard shortcut that is perhaps amongst the most useful in Firefox… Command-Shift-T . Yes that’s all you need, the next time you accidentally close a tab and you want it back, simply hit Command-Shift-T and the tab will magically reappear again! Now that you know it, try to live without it.

Want more Firefox tips? Check out 15 must-know Firefox shortcuts and our Firefox tips archive!

For many years I was a die-hard Safari fan, you couldn’t have pulled me away from it… that is, until Firefox came along. Firefox is speedy, secure, and entirely cross platform compatible, and is now my primary web browser of choice. One of the better ways to improve the user experience with any application is by learning some essential keyboard shortcuts, so here are fifteen such shortcuts for Firefox. Whether you are new to Firefox or a long time user, this list of keyboard shortcuts will likely be useful to you.

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One of my biggest peeves with Firefox 2 is how the tab system works with the scroll bar. Prior to version 2, tabs would squish in size to accommodate more. Being a tab heavy user I found this to be perfectly adequate and I got used to how it works. Enter Firefox 2; instead of resizing the tabs, after a certain amount fill up your tab bar they start to go off screen and are accessible through a tab scroll bar. Personally, I hate this scroll bar, so here’s how to get rid of it:

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