Yup, it turns out that Firefox multiprocess mode is disabled on Ubuntu by default. This is because the Ubuntu modifications add-on that comes pre-bundled with the browser is not yet compatible with it.
If the “Ubuntu Modifications” add-on is active it’s almost certain that multi-processing is disabled.
Multiprocess Firefox (which is also known as “Electrolysis” or e10s) separates web content from the Firefox UI processes. This means that when a poorly made web page or web script causes a spike in CPU or memory the rest of the browse, e.g., tabs, buttons and menus, don’t lock up.
Mozilla is rolling out multiprocess support in Firefox in stages, starting with Firefox 48 released last August.
Enabling multiprocess mode isn’t a cure-all for all your browser slowdowns, of course. If you have a really rubbish internet connection you’ll still a really rubbish even with this option turned on.
But if you’re one of those who, like me, tend to notice a perceptible something afflicting the Firefox experience, I recommend giving this tweak a whirl. Kiss goodbye to those nanosecond lags when switching between tabs of heavy media rich websites.
In fact this feature, when combined with another tweak to make Firefox faster, give a compelling glimpse at how Firefox is shaping up to take on Chromium.
Enable Firefox Multiprocess on Ubuntu
First, check whether Firefox multiproccess mode is enabled in your browser. Head to
about:support in a new tab and check the status of the “multiprocess Windows” option:
Chances are you’ll see “0” windows using it because it is “disabled by add-ons”.
Now, if you love the “Ubufox” add-on you can force enable Firefox multiprocess mode. This will ignoring extension incompatibility and, based on a limited burst of usage, things seem to just fine like this.
But the fastest solution for most is just to disable the “Ubuntu Modifications” extension by going to the Tools > Add-ons page and clicking ‘Disable’ next to the add-ons.
Restart the browser as prompted and, when it comes back up, you can check if multi-processing is now enabled:
If the option still lists as “disabled by add-ons” you’ll need to disable more add-ons, or create a force-override user setting.