The "Tracking Protection" doorhanger can be wrongly resized on Linux

[Softvision-MariusComan]

[Affected versions]:

• Unbranded Firefox Beta (59.0b14) Build ID:20180301022608

[Affected Platforms]:

• Ubuntu 16.04 x64

[Prerequisites]:

• Have a new Firefox profile.
• Have the following prefs. in the "about:config" page (If a preference does not exist, please create it):
  • “extensions.legacy.enabled” pref set to “true”;
  • “xpinstall.signatures.required” pref set to “false”;
  • “extensions.tracking_protection_messaging_study.variation_override” pref set to "fast".
• Have the latest "Tracking Protection Messaging Shield Study" add-on (1.0.2) installed.

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites and navigate to any website.
2. Click the the "pageAction Badge" from the right part of the sidebar (if the doorhanger is not already displayed).
3. Move the mouse cursor on any of the doorhanger's margins until it is changed in a resize arrow.
4. Drag the doorhanger's margin and observe the behavior.

[Expected result]:

• Nothing happens.

[Actual result]:

• The doorhanger is resized.

[Notes]:

• The issue is also reproducible with the “extensions.tracking_protection_messaging_study.variation_override” pref set to "private".
• The issue is not reproducible on Windows and Mac.
• Attached a screen recording of the issue:

[biancadanforth]

Hmm... that's really odd. I'm honestly not sure how to triage this one... @gregglind, what do you think? Possibly a P2? It's in Linux only.

[biancadanforth]

Actually, I suggest a P3, since Mossop is not even sure how to fix this or who would know (seems to be a feature of the Linux Windows Manager; the panel should not be resizable in Firefox), and since the intro panel will just dismiss on its own with several other methods outside of direct interaction (location change same tab, window blur, tab change, clicking the pageAction, ...).

[gregglind]

P3, good and horrifying to know.

I love that we are identifying all ways panels can go wrong.