778 bytes, application/vnd.mozilla.xul+xml
353.67 KB, video/webm
>>> My Info: Win7_64, Nightly 47, 32bit, ID 20160229030448 STR_1: 1. Open attached XUL "testcase 1" (using "Remote XUL Manager" extension) 2. Click on the gray area AR: Label's value changed from "j" to "k", but part of letter "j" is still visible ER: Only letter "k" should be displayed after Step 2. STR_2: 1. Open new window. Make sure there's only 1 tab in that window 2. Paste the following url in urlbar, then press Enter: > data:text/html,<html onclick="document.title=document.title=='k'?'j':'k'"><title>j 3. Hover mouse over the 1st tab in that window, hold left mouse button, move mouse pointer to the right by ~20px, then hover mouse over the 1st tab in that window, release left mouse button. 4. Click on the page content (white area) AR: After Step 2 letter "j" is displayed in the tab title, but it's clipped at the left After Step 3 letter "j" magically redraws, and it's no longer clipped. It's ok. After Step 4 label's value changed from "j" to "k", but part of letter "j" is still visible ER: After Step 2 letter "j" should be fully visible After Step 4 only letter "k" should be displayed in the xul label Note: 1) The right component is probably "xul" or some graphics-related. 2) Nightly 2006-06-01 is affected
Created attachment 8726716 [details] testcase 1 - Parts of text in xul labels (e.g. tab titles) poorly redraw.xul
Created attachment 8726718 [details] screencast 1 - Parts of text in xul labels (e.g. tab titles) poorly redraw.webm
Reproducible in Nightly and 43.0.1, discussion focused on XUL, Layout and Tabbed Browsing areas. Setting to Core XUL for final decision/investigation.
This feels like it might be gfx or layout.
Invalidation bug, so layout. Most likely the visual overflow rect that reflow computes for the nsTextBoxFrame isn't actually containing all the pixels that get drawn to.