[Annotations] The large images (greater than 8500px) are no longer displayed on HiDPI screens

[SoftVision-CosminMuntean]

[Notes]:

• I am not sure, but I think that this issue was introduced after the fix for [Annotations] The saved shots looks blurry on "Edit" page #3669 landed.
• I have managed to reproduce it on a MacBook Pro (Retina, 13-inch, Early 2015) and also on Windows 10 using a 4k monitor with DPI scale set to 350%.

[Affected versions]:

• Nightly 60.0a1
• Screenshots 31.3.0

[Affected Platforms]:

• MacBook Pro (Retina, 13-inch, Early 2015)
• Windows 10 x64 (4k monitor with 350% DPI scale)

[Prerequisites]:

• The "xpinstall.signatures.required" boolean pref is set to "false".
• The "extensions.legacy.enabled" boolean pref is set tot "true".
• Have the Screenshots dev version installed on a new clean profile.
• The Screenshots Onboarding tour was already visited.

[Steps to reproduce]:

1. Start the browser with the profile from prerequisites and navigate to imgur.com.
2. Scroll the page in order to load a large amount of content.
3. Save the full page and click the "Edit this image" button.
4. Observe the image.

[Expected result]:

• The image is correctly displayed.

[Actual results]:

• The image is not displayed.

[Additional Notes]:

• Here is a screen recording with the issue: https://goo.gl/YQXkbC

[SoftVision-CosminMuntean]

I have retested this issue on latest Screenshots 32.1.0 dev version and the issue is no longer reproducible. Tested on Windows 10x 64 and Mac Os 10.13.