hi, this change (resetting and removing the "Don't load tabs until selected" preference from the user interface) has been made in preparation for the upcoming change of firefox to a multi-process architecture. while it is still possible to change that behaviour through about:config, it will lead to a poor performance and experience in upcoming firefox releases... Allow Firefox to load multiple tabs in the background

Thanks for the reply, but what on Earth is a multi-process architecture???!!! And why change firefox so that it has poor performance simply by loading all the tabs at once?! This sounds like a backwards step! I don't want to have to click on every tab at start-up, simply to load it - seriously unimpressed.

well, it is going to be an fundamental change in the inner workings of firefox (probably the biggest one in its history so far) and a huge step forward. in the long run each tab will be running in its separate process which will bring great benefits in performance and security. so for example if one tab will be hanging or crashing it can no longer drag the whole browser down with it and all the other tabs can continue to work normally...

Many thanks for the reply.

So, when will this radical change be implemented?

Also, going forward, in the future does it mean that I'll never be able to select to load tabs automatically - that I'll always have to click on every single tab just to load it...?

the first iteration of e10s (that's the codename for this multi-process firefox project) might roll out to a fraction of users starting with firefox 48: https://asadotzler.com/2016/06/06/firefox-48-beta-release-and-e10s/

as mentioned in the article linked in the first reply, you can still set the old behaviour but it will lead to a bad experience at the launch of firefox in the future, so please keep that in mind.

OK, thanks for the helpful email, but I still think this represents a HUGE backwards step if simply having firefox launch all tabs at once will make it a "bad experience" - I think I'll go try another browser instead. Thanks anyway!

The "Don't load tabs until selected" setting was removed in Firefox 47+ to prevent performance issues with restoring all tabs automatically with multi-process enabled. You can still modify the related prefs on the about:config page in current releases if you are willing to accept possible performance issues when multi-process is enabled.

• browser.sessionstore.restore_on_demand (true)
• browser.sessionstore.restore_pinned_tabs_on_demand (false)

Thanks for your reply cor-el. So, I understand loading all tabs automatically on start-up will make the new firefox unstable (a definite backwards step, in my opinion). BUT, will firefox also be unstable if I launch it, and then click on each of the tabs to load them...?

What do you mean with 'unstable'?

Does Firefox temporarily become unresponsive (hang) or are there other problems?

Sorry, you mis-understand me - in your original post you told me: "The "Don't load tabs until selected" setting was removed in Firefox 47+ to prevent performance issues." So, what you're saying is that loading all tabs on start-up will lead to performance issues - in other words, make it unstable. So, to re-word my question:

I understand loading all tabs automatically on start-up will lead to performance issues with the new firefox (a definite backwards step, in my opinion). BUT, going forward, will firefox also have performance issues if I launch it, and then click on each of the tabs to load them...?

In current Firefox releases is multi-process tabs still disabled and only nightly builds (Nightly, Developer Edition) have a checkbox in about:preferences#general to enable this feature, so there is probably no reason not to load all tabs on startup if you would want to disable this feature. If it is only about a few tabs then you won't notice performance issues. Only with tens of tabs open and a possible forced restart you will notice this.

See also: https://support.mozilla.org/kb/allow-firefox-load-multiple-tabs-background