Wrong screenshot is performed for a selection smaller than 40 px width

[Softvision-CristinaBadescu]

[Notes]:

• Also, the selection is not visible if the width is smaller than 40 px.

[Affected versions]:

• Firefox Beta 58.0b12
• Firefox Nightly 59.0a1
• Screenshots 25.0.0

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Steps to reproduce]:

1. Open Firefox browser and navigate to a website.
2. Click the "Page actions" menu and select Firefox Screenshots.
3. Perform a selection with a width smaller than 40px.
4. Observe the size of the performed selection.

[Expected result]:

• The screenshot is correctly performed, with the selected size.

[Actual result]:

• A wrong screenshot is performed, with a different size.

[Additional notes]:

• Here is a screen recording of the issue:
  

[ghost]

This is odd - the eyes aren't following the mouse.

[Softvision-CristinaBadescu]

I've tested this issue and is no longer reproducible for the width limit (40px) but is reproducible for a selection smaller than 40px height, using latest Firefox Screenshots v28.0.0 installed from here, on latest Nightly build 59.0a1 (2018-01-14), on Windows 10 x64, Mac 10.12.6 and Arch Linux 4.12.

@ianb, @chenba, considering that this issue is reproducible for a selection smaller than 40px height, should I reopen this bug or should I file a new one and track it there?

Here is a screen recording with this behavior:

[chenba]

It's by design that the drag selection does not start until the mouse has traveled more than 40px. The bug here is that the pre-selection on the element where the mousedown occurred is not canceled once the user started dragging.

@Softvision-CristinaBadescu I'll file another bug for it. Thanks.