occasional freeze after a click on the Run button

[grahamperrin]

Occasionally (rarely, touch wood), various things freeze after a click on the run button.

Symptoms are extraordinary; not limited to the browser. Whilst I can Alt-Tab to switch between applications (e.g. to bring something other than Waterfox to front), I can not bring anything to the front by clicking on it; and clicks in panels (of KDE) seem to be not recognised.

It's necessary to terminate the browser process, and then (AFAICT) everything else that was apparently frozen will begin responding.

Example A

KDE Plasma 5 from (bleeding edge) Area 51, XRender for compositing.

After killing plasmashell:

Example B

Xfce in lieu of KDE.

Environment

Periodic tracking disabled.

gfx.xrender.enabled true

browser.tabs.remote.force-disable true

Waterfox 56.0.1 on an outdated (and bleeding edge) FreeBSD-CURRENT.

[grahamperrin@momh167-gjp4-hpelitebook8570p-freebsd] ~% date ; uname -v
Sat 30 Dec 2017 00:41:01 GMT
FreeBSD 12.0-CURRENT #0 r320869: Mon Jul 10 13:57:55 UTC 2017     [email protected]:/usr/obj/usr/src/sys/GENERIC 
[grahamperrin@momh167-gjp4-hpelitebook8570p-freebsd] ~% pkg info waterfox
waterfox-56.0.1.s20171212_2
Name           : waterfox
Version        : 56.0.1.s20171212_2                                                                                                           
Installed on   : Fri Dec 29 10:31:49 2017 GMT                                                                                                 
Origin         : www/waterfox                                                                                                                 
Architecture   : FreeBSD:12:amd64                                                                                                             
Prefix         : /usr/local                                                                                                                   
Categories     : ipv6 www                                                                                                                     
Licenses       :                                                                                                                              
Maintainer     : [email protected]                                                                                                           
WWW            : https://www.waterfoxproject.org/                                                                                             
Comment        : Distilled fork of Firefox                                                                                                    
Options        :                                                                                                                              
        ALSA           : on                                                                                                                    
        BUNDLED_CAIRO  : on
        CANBERRA       : off
        DBUS           : on
        DEBUG          : off
        DTRACE         : on
        FFMPEG         : on
        GCONF          : on
        INTEGER_SAMPLES: off
        JACK           : on
        LIBPROXY       : off
        OPTIMIZED_CFLAGS: on
        PROFILE        : on
        PULSEAUDIO     : on
        SNDIO          : off
        TEST           : off
Shared Libs required:
        libdbus-glib-1.so.2
        libgtk-x11-2.0.so.0
        libXext.so.6
        libpango-1.0.so.0
        libjpeg.so.8
        libpixman-1.so.0
        libsqlite3.so.0
        libcairo.so.2
        libgtk-3.so.0
        libffi.so.6
        libxcb-shm.so.0
        libX11-xcb.so.1
        libfreetype.so.6
        libcairo-gobject.so.2
        libatk-1.0.so.0
        libhunspell-1.6.so.0
        libevent-2.1.so.6
        libvpx.so.4
        libplc4.so
        libXcomposite.so.1
        libxcb.so.1
        libgdk_pixbuf-2.0.so.0
        libgio-2.0.so.0
        libssl3.so
        libXfixes.so.3
        libnss3.so
        libogg.so.0
        libv4l2.so.0
        libgobject-2.0.so.0
        libnssutil3.so
        libplds4.so
        libharfbuzz.so.0
        libstartup-notification-1.so.0
        libX11.so.6
        libdbus-1.so.3
        libXdamage.so.1
        libnspr4.so
        libXt.so.6
        libgraphite2.so.3
        libicuuc.so.60
        libpng16.so.16
        libicui18n.so.60
        libvorbis.so.0
        libglib-2.0.so.0
        libfontconfig.so.1
        libsmime3.so
        libgdk-x11-2.0.so.0
        libgdk-3.so.0
        libXrender.so.1
Annotations    :
        cpe            : cpe:2.3:a:mozilla:waterfox:56.0.1.s20171212:::::freebsd12:x64:2
        deprecated     : Temporary experiment
        expiration_date: 2018-01-30
        no_provide_shlib: yes
        repo_type      : binary
        repository     : FreeBSD
Flat size      : 213MiB
Description    :
The Waterfox source code is a specialised modification of the Mozilla
platform, designed for privacy and user choice in mind. You should be
able to install it and compile Waterfox without any issues. Other
modifications and patches that are more upstream have been implemented
as well to fix any compatibility/security issues that Mozilla may lag
behind in implementing (usually due to not being high priority). High
request features removed by Mozilla but wanted by users are retained
(if they aren't removed due to security).

Features:

 o Disabled Encrypted Media Extensions (EME)
 o Disabled Web Runtime (deprecated as of 2015)
 o Removed Pocket
 o Removed Telemetry
 o Removed data collection
 o Removed startup profiling
 o Allow running of all 64-Bit NPAPI plugins
 o Allow running of unsigned extensions
 o Removal of Sponsored Tiles on New Tab Page
 o Addition of Duplicate Tab option (toggle with browser.tabs.duplicateTab)
 o Locale selector in about:preferences > General
 o Cookie Prompt

WWW: https://www.waterfoxproject.org/

(Yeah, the bleeding edge mixture is eyebrow-raising, but it's remarkably solid. Symptoms of this issue are truly extraordinary.)