Solution: slow Firefox browser slows down the entire Mac

Firefox Logo

I don't know how often I wanted to send the Firefox browser to nirvana because it has become so incredibly slow that you get the feeling that the Mac has to copy 20 GB of data to 5 different hard drives at the same time and the startup volume is full has become. Every few seconds it hangs up for a few seconds and then you can continue. The scrolling gets stuck and the keyboard entries only arrive in the editor in several stages.

What the Mac can do at the same time ...

It happened again today when I wrote the article about the Thunderbolt docks. I had a number of windows open in the background and an external monitor on my MacBook Pro, which was also full of windows. Basically, the MacBook Retina can handle a lot. Videos in Final Cut Pro Rendering and stitching together with Autopano Giga Panoramas is no problem. Even if both are running in the background and I am writing a few emails on the side, the smooth work does not disturb. But obviously Firefox is much more stressful than adding 2 GB of panoramas together. :(

Unfortunately, the browser change is not debatable

One could now say “Don't be shy, just use Google Chrome or Safari!”. Yes, you could say... but if you have installed a number of addons that are simply not available for Safari and Chrome - like me - then it's not that easy to switch. I need the addons for my work and that's why I've had Firefox as my default for what feels like a decadeBrowser. So you can't switch!

Firefox disables multithreading! ??

Firefox Logo
A nice browser with quirks: Firefox.

I've often had the feeling that the guys from the Mozilla Foundation somehow managed to get Firefox to turn off multithreading and everything CPU Power usurps. It's strange what's happening there. The phenomenon has been with me on several Mac OS X and Firefox versions and to date it doesn't seem to have been fixed. But today I've really had enough. After I finished writing my article, I got to the bottom of the matter.

My first tip in such cases would always be that the [Mac's startup volume full-> mac-startup volume-full] is. When that happens, the system becomes really extremely slow. But since I still have over 50 GB free, that couldn't be the case. Also the random access memory was not really busy with 10% according to [iStats Menu-> istats-menu]. So there was only the CPU leftthat maybe somehow at the limit.

Activity indicator: 1/4 of the CPU power goes to Firefox plugin content

A look at the Activity indicator – found under /Applications/Utilities/Activity Monitor – showed me that a process called “Firefox” was using a whopping 28,2% CPU load and another process called “Firefox Plugin Content (Shockwave Flash)” an additional 26,2% fried. It's amazing what's going on in the background.

Activity monitor Firefox
The activity display provides quick information about the processes that are currently using the computing power. Firefox does it twice.

Now it was time to test. I quickly killed the process by marking it and then clicking on the button with the cross in the top left of the display. Then another window comes up or you want to "Quit" or "Quit". I used “quit” and after 2 seconds the process was gone and Firefox was “fast” again.

End the Firefox content process
With a click at the top left, the CPU-demanding process in the activity monitor is switched off.

With that the villain was already found. It is the plugin that is responsible for displaying Flash content on websites. Now I also know why Steve Jobs NEVER wanted Flash on his iPhone. He was so right ...

Solution: Uninstall or deactivate the Flash plug-in

Since I only class Flash as a useless website decoration anyway, I can't really be wrong if I throw it out. To do this, type “about:addons” in the address bar in Firefox. After that, a list of the plugins that are installed in Firefox will appear. Unfortunately, it's not that easy to uninstall (an article on how to do it will be coming soon), but in our case it's enough to deactivate it. To do this, we look for the “Shockwave Flash” plugin and then click on “Never activate” on the right where it says “Always activate”. Now restart Firefox.

The process only starts for certain websites

I just noticed during testing that the "Firefox Content Plugin" process does not start immediately with Firefox, but only becomes visible in the activity monitor when you call up certain websites. This happens to me, for example, when I call up subpages of, such as:

Activity monitor filter Firefox
The text filter at the top right can be used to limit the display to certain processes. As you can see, the Shockwave Flash process no longer works for me.

Try it yourself and watch the activity monitor. You can type “Firefox” in the text filter at the top right. Then only the processes "Firefox" and "Firefox Content Plugin" are displayed and you can quickly see whether the plugin is deactivated or not.

So, now a non-alcoholic beer on a quick Firefox! :)

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3 comments on “Solution: slow Firefox browser slows down the entire Mac”

  1. Thanks for your detailed explanation. Even so, Firefox is far from going well. CPU utilization is still between 35% - 50% and just hangs on every corner. What else can you do ?

    Chrome, on the other hand, runs totally smooth, but I just rely on Firefox :(

  2. I prefer to work with the Chrome browser. I think the browser works well and, especially as a developer, the developer function is really very useful.

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