Text size is not changed to 14, if the sidebar contains paragraphs of different sizes including 14

[Softvision-MariusComan]

[Notes]:

• The issue is reproducible only if you select the 14 font size value.
• The issue is not reproducible if the content does not contain a string of 14 font size value.

[Affected versions]:

• Firefox 56 and up

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Prerequisites]:

• Have a Firefox profile with the latest "Firefox Notes" add-on version (1.9.0dev custom build from 11.06.2017) installed.
• Have content with multiple text sizes, including the default 14 value.

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites.
2. Focus the sidebar and press "Ctrl+A".
3. Click the "Font Size" button.
4. Click 14 and observe the content.

[Expected result]:

• All content is changed to font size 14.

[Actual result]:

• Nothing happens.

[Additional Notes]:

• The issue is reproducible with the "Firefox Notes" version from TxP.
• Attached a screen recording of the issue:
  

[vladikoff]

This is fixed with CKEditor 👍 via #394

[Softvision-MariusComan]

The issue is no longer reproducible on the latest version of Firefox Notes (1.9.0dev custom built on 11.22.2017) on the latest Firefox release and Nightly.