[REGRESSION]: Screenshots different in Firefox on 1.33 due to mouse position

[thewilkybarkid]

Context:

• GOOD Playwright Version: 1.32.3
• BAD Playwright Version: 1.33.0
• Operating System: Docker image
• Extra: Mac Host

We have a bunch of screenshot comparisons starting to fail in 1.33.0 only in Firefox; an example is:

• code
• trace.zip
• video.webm

When it gets through to the "Sorry, we're having problems" page, the "Privacy Policy" link in the footer has an extra thick underline: this is the hover style on links, which is unexpected.

It seems that the position of the mouse has remained unchanged from clicking on the "Start now" button (the log-in form is completed entirely using the keyboard), and it happens that the "Privacy Policy" link is in the same place in the viewport. This didn't happen previously in Firefox, and doesn't happen in the other browers.

If I add a await page.mouse.move(0, 0) before taking the screenshot, the link is not hovered and the test passes as expected.

[thewilkybarkid]

I've just taken a trace with it passing on 1.32.3:

trace.zip
video.webm

There is a difference with clicking the "Start now" button: it scrolls before doing so. This means the link is in a different place. I will try to confirm if there is a behaviour change or if Firefox was always doing this (and this happens to be the first time I've triggered it).

[thewilkybarkid]

I've confirmed that this isn't a regression: Firefox in 1.32.3 was doing the same.

I've fiddled the page to contain lots of links and see the hover appearing:

trace.zip
video.webm

FWIW, this is the trace from Chromium (where it doesn't hover):

trace.zip
video.webm

After using Locator.click(), what is the expectation around the mouse's position? (And when taking screenshots?)

[yury-s]

Can you extract the failing test in a standalone example which we could run locally?

[aslushnikov]

Chris Wilkinson (@thewilkybarkid) ah yes, in 1.33 we fixed a bug when we were always scrolling in Firefox before clicking, even when there was no need to.

Now, in firefox we also have a very trustworthy mouse emulation; so when the page navigates, the mouse stays in place, triggering underlying hover effects. If you do the same manually, as a human, you'll see the same behavior.

Let us see what we can do here. But a quick workaround would be to move mouse away before taking screenshot.

[aslushnikov]

We discussed this, and since this is how the stable firefox works, we decided to keep this as-is. So the workaround would be to move the mouse in this particular test to remove the hover (or to re-baseline with the hover).

Sorry for the inconvenience!