Firefox 4 extensions won't install on Mac OS X

Bill Detwiler overcomes two problems installing Firefox 4--Cisco AnyConnect stops the Firefox installation and corrupt files prevent extensions from installing.

Like millions of others, I downloaded Firefox 4 this past Tuesday. I've been using Mozilla's browser for years, and it's still my favorite--despite Microsoft's significant improvements in IE and Google's release of Chrome.

Unfortunately, this Firefox update didn't go as smoothly as the previous ones. First, the application wouldn't install. Then, I couldn't get any extensions to install. Despite scouring the Internet and Mozilla's support site for several hours, I wasn't able to find a definitive solution. My searching did however, uncover several clues that eventually lead me to the answer. Here's what happened.

Firefox 4 won't install

I was running Firefox 3 (with all the latest updates) on an Intel-based MacBook Pro running OS 10.5.8. I downloaded and mounted the Firefox 4.0.dmg image file from Mozilla's website.

Firefox 4 Installation - Mac OS X

When prompted, I attempt to drag the Firefox application folder ( from the image to the Applications folder. The process started, but the following warning message appeared:

Firefox installation libsmime3.dylib error

As this file was located within my current Firefox application folder, which I was replacing anyway, I quickly tossed the file into the Trash bin. Unfortunately, I was greeted with at least two more warning messages about similar files. At that point, I chucked the whole folder in the Trash.

But, when I went to empty the Trash, I was again told that the offending files were in use.

I figured a reboot was in order. Why? Since the files were no longer in their original location, whatever application was using them wouldn't likely be able to do so when I restarted the machine. Luckily this tricked worked. After rebooting the machine and logging into my account, I emptied the Trash and installed Firefox 4 without a hitch.

Note: It wasn't until after I successfully installed Firefox 4, that I discovered my Cisco AnyConnect VPN client was the application holding these files open--even though it wasn't running at the time. While my file-deletion solution worked, I could also have stopped the VPN agent with the terminal command:
sudo killall vpnagentd

Extensions won't install

Then, the real problem appeared. I couldn't install any extensions--one of my favorite things about Firefox. (I won't use Firefox without NoScript, BetterPrivacy, DownThemAll!, and Page Saver Basic.)

I could locate and download the extensions with Firefox's built-in Add-ons Manager, but the installation process would hang every time. After scouring the Web and Mozilla's Firefox Support site, I came and article that suggested deleting the following files:

  • extensions.ini
  • extensions.sqlite
  • extensions.sqlite-journal
  • compatibility.ini

These files are located under the /Library/Application Support/Firefox/Profiles/[random].default folder.

But even after deleting these files and restarting Firefox, I couldn't install my extensions. I then noticed that a folder named "extensions" also existed within the [random].default folder, and it seemed to contain information on lots of old extensions. Figuring the information was corrupt, I moved the whole thing to the Trash and empty the bin.

Voilà! When I restarted Firefox 4, I was able to download and install all my favorite extensions.


Bill Detwiler is Managing Editor of TechRepublic and Tech Pro Research and the host of Cracking Open, CNET and TechRepublic's popular online show. Prior to joining TechRepublic in 2000, Bill was an IT manager, database administrator, and desktop supp...


Actually I prefer Opera over everything out there. It is, by far, the best browser available.


I downloaded the new version the other day and it loaded very quickly with no problems other than a few of my favorite plugins are no longer supported which is a pain. The interface is clean and easy to use and I have experienced none of the problems I see listed here. Every time there is major update I lose a few more plugin and have to wait for them to catch up. Some of the plugin's that failed are no longer needed as they work very well without them. All in all I like it better than 3.

user support
user support

Had a similar problem but received a message something like it couldn't go to the 2nd step of installation because I didn't have permissions even though I was signed on with administrator credentials. Tried putting download in trash, tried a restart. I had to put the old Firefox from the applications folder into the trash before the new version worked. I will have to play with customizing Firefox 4. I have a custom homepage and it moved the location of home to either extreme right or left but I prefer to have it in the center. I will probably have to put in back on the bookmarks toolbar.


I have used Firefox since it was first launched a long time back and have always enjoyed the interface and the flexibility it has provided the end user through addons or plugins. With the installation of Firefox 4 on Mac OSX and Windows 7 (64-bit) I am repeatedly having to restart Firefox in 32 bit mode as there is a message that pops up saying the the plugin I am trying to uses can only run in 32 bit mode. This is no fault of Firefox but rather of the companies that are a little slow on the uptake. You would think in this day and age where most machines are moving to 64 bit developers would be thinking along the 64 bit line. Mike


I get annoyed when software companies make cosmetic changes which interfere with my productivity and add no real value to the use of their product. I am constantly affected by this with my subscription to AutoCAD. You get used to your eyes quickly finding the icon you know does a certain function and then AutoCAD changes the symbol and the colour of the icon and you spend the next few weeks re-programming yourself to find that icon quickly again. Now, we have Firefox doing this. There must be a sub-industry of the software business that make money out of re-designing the visual look of software so that the users think they are getting something new when the guts of the program is basically the same (maybe they are previous auto worker employees). So, I was interested in experiencing a reportedly faster Firefox with the new release and find that it has slowed me down by having to spend time getting its look back to something I am used to and reprogramming myself with the new interface, for example, the right click on a link has changed the order of opening a new tab and opening a new window --what was the design decision behind this?!


There is a 64-bit version but its been in beta forever and has a lot of problems.


The thing I really like about Firefox 4 is the ability to change it and customize it to how you like it...Firefox 4 retained my old preferences from Firefox 3 and it only took a few minutes to move things around to get them how I liked. For me, the upgrade is purely speed based, and not really cosmetic (save for the buttons looking a tad bit different). I really like the tabs being on top now (copying Safari and Chrome), and I really like the OPTIONS you can completely customize the interface...this not something you get with Safari, Chrome or Internet Explorer. Firefox 4 gives you complete control over the interface, while making speed and improvement updates...even if the right-click menu is in a different order, at least the option to either open in a new tab or a new window is still there!

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