1508043 - (Ubuntu 18.04) Text highlight mismatch in view-source when layout.css.devPixelsPerPx is >= 1.2

Status: NEW

(Core :: Layout: Text and Fonts, defect, P3)

Description

[Jani Uusitalo]

Attachment: screenshot 1: highlighted text on the page is not ”rss”

User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:63.0) Gecko/20100101 Firefox/63.0

Steps to reproduce:

1. Open `about:config`, find `layout.css.devPixelsPerPx` and change the value from default (-1.0) to 1.2.
2. Open a view-source view with long lines: `view-source:https://www.youtube.com/user/10asti10`
3. hit Ctrl+f, search for rss
4. using the LMB, try selecting some text, then copy and paste it somewhere


Actual results:

After step 3, the highlighted text on the page is not "rss". The highlight doesn’t even adhere to letter widths (screenshot 1).

After step 4, the pasted text is not even close to what you’ve selected to copy.


Expected results:

For the search to hightlight an occurence of "rss", and for the pasted text to correspond to what I’ve selected from the view-source view.

Comment 1

[Jani Uusitalo]

I first reported this against 62 in Launchpad: https://bugs.launchpad.net/ubuntu/+source/firefox/+bug/1798103

Firefox was since updated to 63 in Ubuntu and the issue remains.

Comment 2

[Adrian Florinescu [:aflorinescu]]

I tried to reproduce with no luck this issue on Ubuntu 16.04 with:
- Firefox 63 canonical version   (63.0 20181023214907)
- Firefox 63.0.3 Mozilla Release (63.0.3 20181114214635)
- Firefox 65.0a1 20181120220133

For step 3 on `view-source:https://www.youtube.com/user/10asti10` with `layout.css.devPixelsPerPx` set to 1.2 I get two "rss" results, the Ctrl+F finds and focuses the first rss and the copy paste works properly.

Jani, what am I missing here?

Comment 3

[Jani Uusitalo]

Adrian: Thanks for taking a look! I'm using Ubuntu 18.04, and that appears to be crucial here: I created a 16.04 VM, installed all in-release updates (including Firefox 63), and just as you, was unable to reproduce the issue. I then upgraded the VM to 18.04 and the bug immediately manifested again.

Comment 4

[Adrian Florinescu [:aflorinescu]]

(In reply to Jani Uusitalo from comment #3)
> I then upgraded the VM to 18.04 and the bug immediately manifested again.

Now that makes sense, reproduced the issue on Ubuntu 18.04.1 with:
-63.0.3   20181114214635
-64.0b11  20181119162153
-65.0a1   20181121220101

So, since this issue cannot be reproduced on Ubuntu 16.04 or Widows 10 or Osx 10.13, I would assume that this is localized to Ubuntu 18.04.

Comment 5

[Jani Uusitalo]

So I did a little more digging, and found that this actually first cropped up in Ubuntu 17.10.

I then ran mozregression (back on 18.04, my main desktop) and here's what it found:

    7:12.48 INFO: Last good revision: 64bab5cbb9b63808d04babfbcfba3175fd99f69d (2017-10-25)
    7:12.48 INFO: First bad revision: aa958b29c149a67fce772f8473e9586e71fbdb46 (2017-10-26)
    7:12.48 INFO: Pushlog:
    https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=64bab5cbb9b63808d04babfbcfba3175fd99f69d&tochange=aa958b29c149a67fce772f8473e9586e71fbdb46

After that "There are no build artifacts on inbound for these changesets (they are probably too old)."

As this was my first time ever using mozregression, I have no idea how useful that was, but if there's some way I can narrow this down further, I'd be happy to.