1413875 - Firefox sometimes doesn't respond to DPI change (Win10)

Status: NEW

(Core :: Widget: Win32, defect, P3)

Description

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

I frequently get into a state where an open Firefox window doesn't respond to a DPI change -- caused by plugging another monitor in, or by connecting/disconnecting from a RDP session.  New windows are created at the proper DPI.

Various STR:
1:
- open Firefox on normal-DPI display
- connect to Firefox machine from high-DPI laptop via RDP
- disconnect from RDP/log in on desktop on normal-DPI display
- result: Firefox window is huge on normal-DPI display

2:
- open Firefox on high-DPI display (e.g. 4K laptop)
- plug in normal-DPI display, make it the only display
- result: Firefox window is huge on normal-DPI display

3: (reverse of #2)
- open Firefox on normal-DPI display plugged in to 4K laptop (with 4K laptop disabled, though it doesn't really matter)
- unplug normal-DPI display
- result: Firefox window is tiny on high-DPI display

None of these reproduce 100%, but they reproduce often enough.  A Firefox restart fixes it, or opening a new window and just using that.  It would be useful to have some logging for the various DPI change notifications that occur to see what's getting stuck/not being handled properly.

Comment 1

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

Just happened in 59, 20171115100050 when disconnecting from a RDP session.  RDP session was at 150%, physical monitor set to 100%.  I logged back in on the physical monitor, and out of the 3 Firefox windows I had open (same instance), two scaled back down to 100% properly, and one stayed at 150%.  RDP is probably the easiest way to reproduce this (just set either end of the connection to a different % scale).