Glitches are displayed when scrolling the customizable time field from the "Pick a Date/Time" panel

[SoftVision-CarmenFat]

[Affected versions]:

• Release 58.0.2 and up
• Snooze Tabs 1.1.0

[Affected Platforms]:

• All Windows

[Prerequisites]:

• Have a Firefox profile with the latest Snooze Tabs add-on version (https://github.com/bwinton/SnoozeTabs/releases/tag/1.1.0) loaded as a temporary add-on.

[Steps to reproduce]:

1. Open the browser with the profile from prerequisite and navigate to a website.
2. Click the "Snooze Tabs" button from the toolbar.
3. Click the "Pick a Date/Time" option and select the customizable time field.
4. Scroll down/up on the "Hours" and "Minutes" scrollbars and observe the behavior.

[Expected result]:

• The hours and minutes numbers are correctly displayed, without glitches.

[Actual result]:

• Glitches are displayed while scrolling up and down and also when hovering the numbers.

[Notes]:

• This is also reproducible with the Snooze Tabs version from Test Pilot.
• Here is a screen recording of the issue: https://goo.gl/uJ2BCd