STR:

1. Open the new print UI
2. Click "more settings" and then "scale", and put your cursor in the "Scale" textfield.
3. Type in 100 with a leading or trailing space. (Pretend you put in the space by accident.)
4. Try to interpret the resulting UI.

ACTUAL RESULTS:
We highlight the field as invalid, with a message saying "Scale must be a value between 10 and 200". And it looks visually like the field contains the value 100, which should be valid.

EXPECTED RESULTS:
Either:

• we should trim whitespace in our parsing/validation
  ... or:
• we should constrain the field to only allow the user to enter numeric input, somehow. (It is a little weird that I can type in a space character at all in this field, or a value like "aaa" for that matter...)

Similarly we reject values like "50%" (including a literal percent character) which feels like a footgun - we should either trim out or forbid the percent character just like we should do for any whitespace that is present.

(The STR produce similar "actual results" for the validated from/to "range" fields that are being added in bug 1653389, too.)

Ideally, these number fields would disallow any character that isn't 0-9.

https://hg.mozilla.org/mozilla-central/rev/21165ed01da8

Can you request Beta uplift.

Comment on attachment 9172441 [details]
Bug 1660060 - Add a keypress listener to the percentScale element. r?emalysz

Beta/Release Uplift Approval Request

• User impact if declined: Users can enter whitespace which invalidates their input. This experience is inconvenient if the whitespace was accidentally entered and can result in a confusing experience for the user trying to change the page scale.
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: No
• Needs manual test from QE?: Yes
• If yes, steps to reproduce: comment 0
• List of other uplifts needed: None
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Not risky since this patch adds a small restriction for certain input (ie: non-numeric characters) from being entered and only impacts the scale input UI component.
• String changes made/needed:

Comment on attachment 9172441 [details]
Bug 1660060 - Add a keypress listener to the percentScale element. r?emalysz

Approved for 81.0b4.

https://hg.mozilla.org/releases/mozilla-beta/rev/dcc7a303edfb

This issue is verified fixed using Firefox 81.0b4 (BuildId:20200829200810) and Firefox 82.0a1 (BuildId:20200831091558) on Windows 10 64bit, macOS 10.14 & Ubuntu 20.04.

Reopening because a second patch is required to handle the start/end page range fields. Sorry, forgot to mark as "leave-open"

Comment on attachment 9173384 [details]
Bug 1660060 - Add a keypress handler to PrintUIControlMixin that prevents invalid input. r?emalysz

Beta/Release Uplift Approval Request

• User impact if declined: Users can enter whitespaces into the copies and page range fields, which invalidates their input. This experience is inconvenient if the whitespace was accidentally entered and can result in a confusing experience for the user trying to change inputs for these fields.
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: No
• Needs manual test from QE?: Yes
• If yes, steps to reproduce: comment0 except test this on the "Copies" and "Pages (Custom)" fields.
• List of other uplifts needed: None
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Not risky since this patch adds a small restriction for certain input (ie: non-numeric characters) from being entered and only impacts the scale input, copies, and page range UI components.
• String changes made/needed:

https://hg.mozilla.org/mozilla-central/rev/4e9e20d085c1

Comment on attachment 9173384 [details]
Bug 1660060 - Add a keypress handler to PrintUIControlMixin that prevents invalid input. r?emalysz

Approved for 81.0b6.

https://hg.mozilla.org/releases/mozilla-beta/rev/69c7cdb099f8

This is verified fixed using Firefox 81.0b8 (BuildId:20200908191057) on Windows 10 64bit, macOS 10.14 & Ubuntu 18.04 64bit.