Firefox appears horribly distorted after upgrade to 38.0

[Pacific Seascape]

Today when I opened my package manager (muon) to check for updates, I saw there was an update for Firefox, to version 38. I installed this along with other available updates like I always do. Upon restarting Firefox, however, I discovered a nasty surprise. All of Firefox's UI was appearing as if I was on a computer with a much lower screen resolution, and web pages were appearing as if I had massively zoomed in on them.

Everything looks many times bigger than it should be: icons, toolbars, tabs, menus, web pages, they're all big.

I have no idea how or why this happened.

I tried restarting Firefox in safe mode, wondering if it was maybe an incompatible add-on. This did absolutely nothing for me. I began to suspect that the update to Firefox 38 had caused the problem. So I decided to test my theory by downgrading. The only prior version in the repos appeared to be 28.x, but luckily, in my /var/cache/apt/archives/ folder, I found the .deb for the last version of Firefox I had installed - 37.0.2. I opened the .deb and installed it. Upon opening Firefox, everything was normal again -no abnormally large chrome or web pages.

I ran the upgrade to Firefox 38 again, and bingo - the problem came back. I ran ubuntu-bug firefox to get Apport going, and then finished up by coming here to Launchpad to submit a report. Attached a screenshot to show the distortion.

My computer's native resolution is 1920x1080, and that's what I run.

I'll have to stick with 37.0.2 until I get some confirmation that this issue with Firefox 38 has been addressed/resolved. Firefox is unusable with this problem.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: firefox 38.0+build3-0ubuntu0.14.04.1
ProcVersionSignature: Ubuntu 3.13.0-52.86-generic 3.13.11-ckt18
Uname: Linux 3.13.0-52-generic x86_64
NonfreeKernelModules: nvidia
AddonCompatCheckDisabled: False
ApportVersion: 2.14.1-0ubuntu3.10
Architecture: amd64
BuildID: 20150511103818
Channel: Unavailable
CurrentDesktop: KDE
Date: Thu May 14 18:22:34 2015
EcryptfsInUse: Yes
Extensions: extensions.sqlite corrupt or missing
ForcedLayersAccel: False
IfupdownConfig:
 # interfaces(5) file used by ifup(8) and ifdown(8)
 auto lo
 iface lo inet loopback
IncompatibleExtensions: Unavailable (corrupt or non-existant compatibility.ini or extensions.sqlite)
InstallationDate: Installed on 2014-07-28 (290 days ago)
InstallationMedia: Kubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2)
IpRoute:
 default via 192.168.1.1 dev eth0 proto static
 172.16.240.0/24 dev vmnet8 proto kernel scope link src 172.16.240.1
 192.168.1.0/24 dev eth0 proto kernel scope link src 192.168.1.21 metric 1
 192.168.66.0/24 dev vmnet1 proto kernel scope link src 192.168.66.1
Locales: extensions.sqlite corrupt or missing
MostRecentCrashID: bp-3c820930-59fa-410c-9358-def442150515
Plugins: Shockwave Flash - /usr/lib/flashplugin-installer/libflashplayer.so
PrefSources:
 prefs.js
 [Profile]/extensions/{11b496ea-481a-11dc-8314-0800200c9a66}/defaults/preferences/shooter.js
 [Profile]/<email address hidden>/defaults/preferences/fvd_single_setup.js
 [Profile]/<email address hidden>/defaults/preferences/preferences.js
Profiles: Profile0 (Default) - LastVersion=38.0/20150511103818 (In use)
RfKill:
 0: phy0: Wireless LAN
  Soft blocked: yes
  Hard blocked: no
RunningIncompatibleAddons: False
SourcePackage: firefox
Themes: extensions.sqlite corrupt or missing
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 12/23/2011
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: E16F2IG6 V3.0R
dmi.board.asset.tag: To be filled by O.E.M.
dmi.board.name: MS-16F2
dmi.board.vendor: Micro-Star International Co., Ltd.
dmi.board.version: To be filled by O.E.M.
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 10
dmi.chassis.vendor: Micro-Star International
dmi.chassis.version: To be filled by O.E.M.
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrE16F2IG6V3.0R:bd12/23/2011:svn:pn:pvrTobefilledbyO.E.M.:rvnMicro-StarInternationalCo.,Ltd.:rnMS-16F2:rvrTobefilledbyO.E.M.:cvnMicro-StarInternational:ct10:cvrTobefilledbyO.E.M.:
dmi.product.version: To be filled by O.E.M.

[madbiologist (me-again)]

According to your system info, you have dmi.chassis.type: 10, which is a notebook. What brand and model of notebook is it?

Try adjusting Firefox's setting for High DPI support, which operates as a global zoom factor:

(1) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.

(2) In the filter box, type or paste pix and pause while the list is filtered

(3) The layout.css.devPixelsPerPx preference usually is set to -1.0 which means use the system default. You can change that to 1.0 for 96-dpi dispay and see whether that is what you prefer. And you can increase the size from there in increments, for example, 1.1 for a global "110%" zoom.

Please be careful not to set this value to something tiny, as it can be hard to recover from that.

[Pacific Seascape (seascape)]

This is a ZaReason Verix 2.5 notebook, designed for use with Ubuntu (and Kubuntu). However, it is typically used like a desktop, connected to peripherals including a large display and keyboard/mouse.

Setting layout.css.devPixelsPerPx to 1.0 does reset the Firefox user interface back to what it is supposed to be. I'll be able to stay on the latest version (39.x) now.

But I'm mystified: Firefox has been set to use the system default for a long time... since Trusty was installed on this system, actually. Prior to version 38, -1 had the same effect as the 1.0 setting you suggested.

But as of version 38, -1 suddenly became equivalent to something higher -- maybe 1.5. What's up with that?

[madbiologist (me-again)]

All I could find was an article at http://www.omgubuntu.co.uk/2015/05/firefox-38-arrives-with-tab-based-preferences-ruby-character-support which mentions near the end:

"Improved HiDPI on Linux, with scale now set by DPI (previously defaulted to 1)".

They don't really explain that and it seems to conflict with your comment that "Firefox has been set to use the system default for a long time... since Trusty was installed on this system, actually. Prior to version 38, -1 had the same effect as the 1.0 setting you suggested." Perhaps that preference was actually ignored/overridden until Firefox 38? I don't know.

I don't need to adjust the layout.css.devPixelsPerPx preference on my system. When I open a command prompt and type "xdpyinfo | grep dots" I get the result "resolution: 96x96 dots per inch". What do you get?

[Pacific Seascape (seascape)]

Result:

$ xdpyinfo | grep dots
resolution: 144x144 dots per inch

HiDPI support just made its way into Mozilla Thunderbird (as of version 38.2.0), and when I opened Thunderbird, the whole UI was appearing large and distorted. But setting layout.css.devPixelsPerPx to 1.0 with the config editor quickly put Thunderbird back to normal, same as with Firefox.

[Paul White (paulw2u)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. We are sorry that we do not always have the capacity to look at all reported bugs in a timely manner. There have been many changes in Ubuntu since that time you reported the bug and your problem may have been fixed with some of the updates. It would help us a lot if you could test it on a currently supported Ubuntu version.

When you test it and it is still an issue, kindly upload the updated logs by running only once:

apport-collect 1455286

and any other logs that are relevant for this particular issue.

[Launchpad Janitor (janitor)]

[Expired for firefox (Ubuntu) because there has been no activity for 60 days.]