Bugzilla

Hi, the easiest way to reproduce the problem is to run Firefox on a high-DPI screen laptop, and maximize the browser.
Then, open this link:
https://gistpreview.github.io/?dcccceb93a87316fcf455f7786ddb333
and while it's loading, try to open a new tab by clicking the '+' button in the Tab Bar.
The bug is that the UI will not respond, in fact the '+' won't even highlight as you mouse-over, for several seconds, until the page stops loading.  The duration of the lock-up is not always consistent, but it would be a poor user experience most of the time.
Likewise if you go back and forth between the tabs and hit refresh on the above page, the UI is slow to respond.  With the fix, there can be some sluggishness under load but it should be orders of magnitude better.

The key part is the high number of pixels to draw due to high-resolution monitor and large browser window on a not-super-powerful platform.

You should be able to reproduce the original problem somewhat by going to `about:config` and setting `gfx.webrender.enable-low-priority-pool` to `false` and restarting the browser.

Hi, the easiest way to reproduce the problem is to run Firefox on a high-DPI screen laptop, and maximize the browser.
Then, open this link:
https://gistpreview.github.io/?dcccceb93a87316fcf455f7786ddb333
and while it's loading, try to open a new tab by clicking the '+' button in the Tab Bar.
The bug is that the UI will not respond, in fact the '+' won't even highlight as you mouse-over, for several seconds, until the page stops loading.  The duration of the lock-up is not always consistent, but it would be a poor user experience most of the time.
Likewise if you go back and forth between the tabs and hit refresh on the above page, the UI is slow to respond.
Even with the fix, there can still be some sluggishness under load but it should be orders of magnitude better.

The key part is the high number of pixels to draw due to high-resolution monitor and large browser window on a not-super-powerful platform.

You should be able to reproduce the original problem somewhat by going to `about:config` and setting `gfx.webrender.enable-low-priority-pool` to `false` and restarting the browser.