Firefox's unloaded tab handling got a whole lot better

Martin Brinkmann
Jul 23, 2017

Starting with Firefox 55, scheduled for an August 8th, 2017 release, unloaded tab handling in the Firefox web browser got a whole lot better.

This should have a positive impact on all Firefox users who restore the last browsing session on start of the browser. It improves the time it takes to load the browser and also the memory consumption.

To hammer home the point, Mozilla employee Dietrich Ayala ran a test with a Firefox profile with 1691 open tabs in the browsing session.

Note: Startup time depends on a number of factors. All Firefox users who load the previous browsing tab on start should see an improvement in startup time and memory use. As a rule of thumb, the more tabs get loaded, the better the improvement.

He tested startup time and memory performance of Firefox 20, 30, 40, and 50 to 56 using that profile. He could not test the profile in Firefox 10 as it would hang and not load the profile at all.

firefox startup improvement

His main findings are that startup time increased significantly from Firefox 20 to Firefox 51, decreased in Firefox 52 to 54, and then fell sharply to the lowest ever value in Firefox 55.

The startup time was at its highest in Firefox 51 which took more than 7 minutes to start the browser. Firefox 52 took more than 5 minutes to start up loading the profile, and Firefox 55 only 15 seconds.

For memory usage, the findings where equally impressive. Memory usage increased up until Firefox 54, and fell sharply in Firefox 55.

Firefox 50 to 54 used about 2 Gigabytes of RAM when loading the profile. The memory usage dropped to less than 0.5 Gigabytes in Firefox 55.

Remember that this is for tabs that are not fully loaded (read inactive). Firefox won't load all websites in all tabs by default on session restore. This is different from Google Chrome which loads all tabs on session restore. Chrome users will notice that the browser will be largely unresponsive during that time.

Chrome does not ship with a native option to load tabs on activation during start. Chrome users may use an extension like Native Lazy Tabs for Chrome to enable this functionality.

Mozilla's work on improving the loading of tabs on browser start continues. Firefox users interested in the progress that Mozilla engineers make may want to monitor Bug 906076 on Bugzilla@Mozilla.

Closing Words

The improvements are certainly impressive but that many tabs are an edge case. Still, it highlights that Firefox's startup got a whole lot better in terms of memory use and startup time when the last browsing session is loaded.

I'd like to know what made the startup time and memory use increase by this much in the past. Which changes were made that impacted it negatively?

Now You: What's the startup time of your browser? Do you load all tabs or lazy load tabs?

Firefox's unloaded tab handling got a whole lot better
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Firefox's unloaded tab handling got a whole lot better
Starting with Firefox 55, scheduled for an August 8th, 2017 release, unloaded tab handling in the Firefox web browser got a whole lot better.
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  1. Jeff said on July 29, 2017 at 8:29 pm

    Thanks for covering this Martin. I am happy that Firefox startup time has improved this much!

  2. pd said on July 24, 2017 at 4:08 pm

    Martin I think you may want to define “load” in this case. Presumably all this means is the browser UI becomes usable in that it’s not locked from user input by the creation of all those tabs and the relevant history and so forth.

    Actually “loading” a usable web page wouldn’t happen – beyond a handful (whatever the default is) – until the user activates the tabs beyond the default number, would it?

    I think it’s important to note this distinguishment between ‘setting up’ or ‘re-instating’ of ‘parked/inactive/unloaded tabs’ versus actually loading 1691 entire web pages/sites/apps inside 15 seconds. Even a mature Servo/e10s based Firefox running on a RyZen Threadripper with a T1 connection to the web would not manage that :)

    FWIW, I imagine *most* users/ghacks readers would not expect 1691 tabs to fully load in 15 seconds but I suspect it may help to clarify this for the less informed or new readers.

    1. Martin Brinkmann said on July 24, 2017 at 4:39 pm

      PD you are right. Loading does not mean that the content of the tabs is loaded, I think of it as a shell that gets loaded.

  3. jimbo said on July 24, 2017 at 12:25 pm

    If using a lot of tabs worth using addon like OneTab (Chrome version best) to periodically save all tabs into a neat manageable list.

  4. Paul(us) said on July 24, 2017 at 12:10 pm

    Martin, in your informative – and well-written article (could somebody ask for more?) you are mentioning that “Chrome does not ship with a native option to load tabs on activation during start. Chrome users may use an extension like Native Lazy Tabs for Chrome to enable this functionality.”
    But did you know that this Native lazy tab is not working in private modes?
    So could you say that this Native lazy tab is only parcely working? Is it a bit lazy? :-)

  5. Ben said on July 24, 2017 at 11:49 am

    Have this update for some weeks now, for me it’s pretty much the best update they did in the past 12 years.
    But makes me wonder at the same time, why did it take them so long – I mean the idea of not running every addon on every unloaded tab, is kinda obvious.
    Sadly in FF 56 they also introduced parts of their new very shitty UI – it’s a pain to use it compared to the old one.

  6. Troppo said on July 24, 2017 at 9:33 am

    Now that’s a feature a power user can get behind :)

  7. Richard Allen said on July 24, 2017 at 8:15 am

    I’ve noticed with Nightly that Mozilla has FINALLY made some progress improving startup time. Started using FF the day v3 was released and startup time has steadily deteriorated since then, unless of course you are fortunate enough to have had a significant hardware upgrade every other year. About a year after FF v3 was released Pale Moon was released and from that day the difference in browser startup time and memory use has steadily grown over the years. Right now the difference is kind of substantial. Nightly is finally after many years the first version of FF to match or exceed Pale Moon in startup time. I personally didn’t think it would ever happen because it’s been so long. Can’t decide if Mozilla should be praised for the improvement or cursed for taking so long, I’m leaning towards both. ;)

    Not including IE11, I have 5 browsers installed. They all have uBO, Greasemonkey and Stylish installed or a webext equivalent, plus other extensions. All browsers are 64 bit except Pale Moon. All open with one tab and I use either the
    session manager built into the browser or the one in Tab Mix Plus.

    Chrome Beta – 7 ext – 1.95 sec startup time.
    Nightly – 5 ext – 2.1 sec.
    Pale Moon – 17 ext – 2.2 sec.
    Vivaldi snapshot – 7 ext – 2.3 sec.
    Firefox v54 -13 ext – 3.1 sec.

    1. Troppo said on July 24, 2017 at 9:28 am

      There’s a one second difference for the best versus worst scores. I don’t care about such a tiny difference, even the guys who most often close and reopen their browser don’t do it more than say 10 times a day.

      However with 40 tabs it’s more like 15 seconds reduced to let’s say 3 in Firefox 55. THAT’S noticeable, and that’s what should be compared. If you do that with Chrome Beta while being offline, what is the score that you get ? Then do it for Firefox 54 and 55.

      That said, if opening browser could be instant that would of course be pleasant, but a 1 second difference is definitely not a factor in browser selection at all IMO.

      Not even a 15 seconds difference is, objectively, if I can have a workflow where I only open/close once or twice a day there’s no reason it should matter. But nothing is objective, and such a difference leaves an impression on the user that arguably participates in the overall impression they have of the browser. So it’s better to fix it.

  8. John said on July 24, 2017 at 6:36 am

    Firefox 55 will be a great version because it consolidates changes from two channels (nightly and the depreciated aurora).

    From what I’m seeing, Firefox keeps getting better while Chrome doesn’t improve anything. In fact, Chrome is only getting worse day by day.

    The fact that it’s the only browser that doesn’t have the lazy tabs feature is laughable.

    1. Deo et Patiae said on July 24, 2017 at 11:42 am

      One more thing I’d like in Firefox is to suspend OS-Wise the inactive Tabs. It’s a must and truly saves a lot of resources. If they truly implement it correclty OS-System-Wise [( like all win10 apps behave ) including Edge ] woulld me amazing. Responsive af with all the benefits this provides.

    2. OldAgeGranny said on July 24, 2017 at 11:09 am

      Chromes only getting better, Firefox im unsure of as the WE API is not stable to the point of bothering using fiorefox beyond 57 an beyond

    3. TianlanSha said on July 24, 2017 at 9:03 am

      I’m using Pale Moon to write this in case you get any funny ideas.

      Firefox only recently started to improve, in version 55 of Chrome, they reduced memory usage by 30%
      Chrome 60 is also about to arrive with performance improvements. Whenever I used Chrome, it’s lighning fast, under whatever strain my computer is in. Yesterday I tried Vivaldi, when I was playing a game, Vivaldi couldn’t even respond when I was switching/creating tabs, nothing like this in Chrome.

      The Mozzilla team decided they need to renovate their browser too little too late and at a great cost. Everyone is using Chrome now, only a few people still use Firefox and that’s because of specific add-ons that won’t work in 57. At that point when Mozilla Firefox finally transforms into Mozilla Chrome, Google Chrome will still be the better Chrome and people will still use it.

      Firefox lost The Browser War long ago, now they’re shooting themselves in the foot, just like Microsoft are with their disaster called Windows 10.

      1. bwat47 said on July 24, 2017 at 4:30 pm

        > only a few people still use Firefox and that’s because of specific add-ons that won’t work in 57.

        [Citation Needed]. Last I recall, the statistics actually show that ~40% of firefox users don’t even use addons:

        And my guess is, of those that do use addons most probably use basic stuff like an adblocker that would have no trouble with webextensons.

        Also afaik firefox’s market share is ~12%. Not as good as it once was, but that’s a hell of a lot more than ‘a few people still using it’…

      2. Troppo said on July 24, 2017 at 9:39 am

        Firefox: Second most used desktop browser in the world; first in Germany.

  9. dmacleo said on July 23, 2017 at 10:07 pm

    never have that many open but often stop/start with 10 tabs. and when I switch to them I want them available immediately so I load them on startup.
    start times (from dead cold windows boot) negligible between no tabs/10 tabs really.

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