[Annotations][Crop] The "Confirm" and "Cancel" buttons don't have tooltips

[SoftVision-CosminMuntean]

[Affected versions]:

• Nightly 59.0a1
• Screenshots 28.0.0 dev

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Prerequisites]:

• The "xpinstall.signatures.required" boolean pref is set to "false".
• The "extensions.legacy.enabled" boolean pref is set tot "true".
• Have the Screenshots 28.0.0 dev version installed from here, on a new clean profile.

[Steps to reproduce]:

1. Open latest Nightly build with the profile from prerequisites and navigate to any website.
2. Perform a selection on the page and save it.
3. Click the "Edit this image" button.
4. Click the "Crop" tool and hover the "Confirm" and "Cancel" buttons.

[Expected result]:

• The "Confirm" and "Cancel" buttons have tooltips.

[Actual result]:

• The "Confirm" and "Cancel" buttons from dont't have tooltips.

[Notes]:

• Here is a screen recording with the issue:
  

[SoftVision-CosminMuntean]

I have retested this issue using latest Firefox Screenshots 28.0.0 dev version and the issue is no longer reproducible. The "Confirm" and "Cancel" buttons have tooltips.
Tested on Windows 7 x64, Mac 10.12 and Arch Linux.