New compositor in Firefox 70

Mozilla has been doing a lot of work to improve the rendering performance and power usage of Firefox. I tested the latest version on a project with ~1300 blocks and drag performance was much smoother on Firefox than on Chrome. I’m curious if others are seeing benefits in App Inventor as well.


I do most of my work on my phone so I just installed Firefox 68.2.0. It does run a bit more smoothly than Chrome.
Thanks for posting!

Absolutely! When I have a project with more than 1500 blocks, I have to use Firefox or it becomes almost impossible to do anything.
I started collapsing all the events and procedures. It helps a lot but it takes time to get adapted to it, after being used to see all the blocks and logic at a glance.
Any plans on improving the rendering?

Based on my findings, on desktop, Firefox uses much less memory than Chrome.

Memory Usage (in MB)

Firefox Chrome (JS) Chrome (Total)
Designer 55 96 235
Blocks editor 98 120 345

Note: The readings are not accurate and are taken from the browser’s Task Manager.

We actually already have done quite a bit on top of what Blockly has, performance-wise. I gave a talk on some of our performance work at Google last month (slides). With our optimizations turned off, we see anywhere from 2-4x slowdown on large projects. Unfortunately they haven’t posted the recording of the talk yet.

Edit: The talks are available


(added to new AppInventor Performance section of FAQ)

For me, Blocks Editor freezes when loading blocks from backpack. Only solution to reload AI2 site. Also, mouse wheel scrolling of blocks editor very very slow (this could be a firefox setting I haven’t found yet!)

I am also seeing a blocks editor freeze when pulling blocks from the palette. A trip to the Designer and back resolved that.

70.0.1 (64-bit)

Do you see the same issues on ai2-test? There were some issues I fixed that aren't yet in production but are on the test server.

ai2-test version fixes items 1 and 3, but no change to mouse wheel scrolling, even after changing settings in Firefox (which work on “normal” web pages)