Mm strange. There's nothing I can think of that may cause slow down.

Are you seeing this issue on Firefox mobile or Firefox desktop and is this just on the Alcatel OneTouch? When I try your site now I'm not noticing anything unusual so this is likely to be a browser specific problem.

Firefox mobile (on mobile device). On firefox desktop emulating a mobile device doesn't cause this issue, but probably because I have a high performance computer.

The problem is noticeable also on chrome mobile, but less significantly.

I suspect the problem is related to the lazy loading of the images, because other pages don't have this issue (and that specific page has lots of them). When I was using MediaWiki 1.29 the images weren't lazyloaded (and there were no slowdown).

Can you disable lazy loading images to see if the problem goes away? Would be useful to know!

wgMFLazyLoadImages = ['base'=>false, 'beta'=>false];

Yep, that's indeed the problem. It opens sections instantly now.

I've done some testing on that page to see if the lazy loading scripts were the culprit.

Here's a profile of the Chrome devtools timeline with cpu throttling of 6x:

• https://gist.githubusercontent.com/joakin/a9c6ed846ec6aa17e3ebc843970a622e/raw/3d68710aba5e289db8c4b42d0157281e010f3853/Profile-20180130T094009.json
• For the URL https://www.wikidex.net/index.php?title=Trapinch&mobileaction=toggle_view_mobile

If you load it you can see that there is a huge style recalculation after expanding the section, so it is possible the lazy loading images code has some impact.

It is strange though, since images smaller than 50px are not lazy loaded, so all those small images shouldn't be even touched by the code.

For reference:

• Section toggling triggers lazy loading: https://github.com/wikimedia/mediawiki-extensions-MobileFrontend/blob/master/resources/mobile.startup/Skin.js#L182
• Which iterates through placeholders https://github.com/wikimedia/mediawiki-extensions-MobileFrontend/blob/master/resources/mobile.startup/Skin.js#L168
  • Not images or small images
  • This are the DOM nodes traversed https://github.com/wikimedia/mediawiki-extensions-MobileFrontend/blob/master/resources/mobile.startup/Skin.js#L128

After all of this, I'm not sure that lazy loading images is actually the culprit of this, there may be some other factor triggering style recalculations on a lot of the DOM but it doesn't make much sense that it is the fault of this feature.

There may be other features introduced in the last version, so maybe something else is the culprit.

Can you test https://www.mediawiki.org/wiki/User:Ciencia_Al_Poder/MinervaTest?useformat=mobile ? I can see it lazy loading the images of the same section. There may be some logic problem on that script and it's not doing what's supposed to do.

@Ciencia_Al_Poder Those two pages are not showing the same images:

• Wikidex, See in Chrome: view-source:https://www.wikidex.net/index.php?title=Trapinch&mobileaction=toggle_view_mobile
  • Find lazy-image-placeholder
  • 0 results
• Your test page, See in Chrome: view-source:https://m.mediawiki.org/wiki/User:Ciencia_Al_Poder/MinervaTest?useformat=mobile
  • Find lazy-image-placeholder
  • 459 results

So your page actually lazy loads the small images while the wikidex one doesn't right now.

I think he enabled skipping lazy loading small images.

From what I've seen, lazy loading small images actually has better performance than not lazy loading them, see these two chrome profiles (6x cpu throttling, galaxy s5 profile, just measuring opening the "Movimientos" section):

• Lazy loading small images, url - profile.json
• Not lazy loading small images, url - profile

So just to understand, does https://www.mediawiki.org/wiki/User:Ciencia_Al_Poder/MinervaTest?useformat=mobile behave performantly on your device now? Or https://www.wikidex.net/index.php?title=Trapinch&mobileaction=toggle_view_mobile ? Or none? Because that may be counter intuitive to the tests I've been running.

If that is the case, we may have to switch to real device analysis for this one.

Indeed, both pages don't display the same images. This is because I wanted to create a test page on a WMF wiki (running a near-master version of MediaWiki and extensions), but also I didn't want to upload all the required images to make the test close to the original problem, so I searched for small images in commons with similar sizes to replace the ones used on our wiki. Note also that the test page on WMF is more simple, as I stripped all internal links (which would render red links otherwise). This of course makes the DOM more simple and may cause a bit gain in performance.

And yes, I've disabled wikidex.net lazy loading images as suggested by Jdlrobson. I can enable it on a test site if you want (will probably do when I arrive at home)

https://www.mediawiki.org/wiki/User:Ciencia_Al_Poder/MinervaTest?useformat=mobile does not behave performantly on my device, or at least not in FIREFOX (latest update).

https://www.wikidex.net/index.php?title=Trapinch&mobileaction=toggle_view_mobile didn't behave performantly before disabling lazy load of images. It now does behave performantly after disabling lazy load of images. Again, on Firefox.

I think it has nothing to do with my device, but with Firefox browser for Android (on a mobile device). On Google Chrome for Android the performance is hardly noticeable. On Firefox for Android it's highly noticeable (1 second aprox. when clicking on the section header until it's opened/closed)

You can test the same page with lazy loaded images enabled here http://test.wikidex.net/index.php?title=Trapinch&useformat=mobile

@Ciencia_Al_Poder could you try turning back on lazy loading images but also set the following:

wgMFLazyLoadSkipSmallImages = true;

I think this will give you the best of both worlds.

Ok, thanks. I've done this and the performance has improved a lot.