Bug#818179: firefox: rgba(0,0,0,0.99) becomes read instead of black

[Olli]

Package: firefox
Version: 45.0-1
Severity: important

Dear Maintainer,
since yesterday I got this strange behavior. All rgba(0,0,0,<opacity value lower 1>) become 
rgba(255,0,0,<opacity value lower 1>).
I've the behavior on all profiles, with or without add-ons and on firefoxs own control elements (while typing in url bar the suggestions become red backgrounded).
I also tried it with the beta and the development release of firefox from mozilla. The development release don't show this behavior.
You may consider take a look at the screenshot http://imgur.com/M8QUTvH - I'd set the background manually and you see the box should be black instead of red. 
The behavior is also showed while using an XUL app called pencil ( https://github.com/prikhi/pencil/ ).
>From gut I don't think it's a bug located in firefox rather in some libs but I don't have an idea which one it coult be.

-- Package-specific info:

-- Extensions information
Name: ADB Helper
Location: ${PROFILE_EXTENSIONS}/adbhelper at mozilla.org
Status: user-disabled

Name: Certificate Patrol
Location: ${PROFILE_EXTENSIONS}/CertPatrol at PSYC.EU.xpi
Status: user-disabled

Name: Default theme
Location: /usr/lib/firefox/browser/extensions/{972ce4c6-7e08-4474-a285-3208198ce6fd}.xpi
Package: firefox
Status: enabled

Name: Firefox Hello Beta
Location: ${PROFILE_EXTENSIONS}/loop at mozilla.org.xpi
Status: enabled

Name: LeechBlock
Location: ${PROFILE_EXTENSIONS}/{a95d8332-e4b4-6e7f-98ac-20b733364387}
Status: enabled

Name: Perspectives
Location: ${PROFILE_EXTENSIONS}/perspectives at cmu.edu
Status: user-disabled

Name: ProxTube - Gesperrte YouTube Videos entsperren
Location: ${PROFILE_EXTENSIONS}/ich at maltegoetz.de.xpi
Status: user-disabled

Name: stealthy
Location: ${PROFILE_EXTENSIONS}/stealthyextension at gmail.com.xpi
Status: user-disabled

Name: Tabgruppen
Location: ${PROFILE_EXTENSIONS}/tabgroups at quicksaver.xpi
Status: enabled

Name: Twitter service
Status: enabled

Name: uBlock Origin
Location: ${PROFILE_EXTENSIONS}/uBlock0 at raymondhill.net.xpi
Status: enabled

Name: United States English Spellchecker dictionary
Location: ${PROFILE_EXTENSIONS}/en-US at dictionaries.addons.mozilla.org
Status: enabled

Name: Valence
Location: ${PROFILE_EXTENSIONS}/fxdevtools-adapters at mozilla.org
Status: user-disabled

Name: Wallabag
Location: ${PROFILE_EXTENSIONS}/poche at gaulupeau.fr.xpi
Status: enabled

Name: Wörterbuch Deutsch (de-DE), Hunspell-unterstützt dictionary
Location: ${PROFILE_EXTENSIONS}/de_DE at dicts.j3e.de
Status: enabled

-- Plugins information
Name: VLC Web Plugin
Location: /usr/lib/mozilla/plugins/libvlcplugin.so
Package: browser-plugin-vlc
Status: enabled


-- Addons package information
ii  browser-plugin 2.0.6-4      amd64        multimedia plugin for web browser
ii  firefox        45.0-1       amd64        Mozilla Firefox web browser

-- System Information:
Debian Release: stretch/sid
  APT prefers unstable
  APT policy: (500, 'unstable'), (500, 'testing'), (500, 'stable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 4.3.0-1-amd64 (SMP w/2 CPU cores)
Locale: LANG=de_DE.utf8, LC_CTYPE=de_DE.utf8 (charmap=UTF-8)
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages firefox depends on:
ii  debianutils               4.7
ii  fontconfig                2.11.0-6.3
ii  libasound2                1.1.0-1
ii  libatk1.0-0               2.18.0-1
ii  libc6                     2.22-3
ii  libcairo2                 1.14.6-1
ii  libdbus-1-3               1.10.8-1
ii  libdbus-glib-1-2          0.106-1
ii  libevent-2.0-5            2.0.21-stable-2+b1
ii  libffi6                   3.2.1-4
ii  libfontconfig1            2.11.0-6.3
ii  libfreetype6              2.6.3-3
ii  libgcc1                   1:5.3.1-11
ii  libgdk-pixbuf2.0-0        2.32.3-1.2
ii  libglib2.0-0              2.46.2-3
ii  libgtk2.0-0               2.24.30-1
ii  libhunspell-1.3-0         1.3.3-4
ii  libnspr4                  2:4.12-1
ii  libnss3                   2:3.23-1
ii  libpango-1.0-0            1.38.1-1
ii  libsqlite3-0              3.11.1-1
ii  libstartup-notification0  0.12-4
ii  libstdc++6                5.3.1-11
ii  libvpx3                   1.5.0-2
ii  libx11-6                  2:1.6.3-1
ii  libxcomposite1            1:0.4.4-1
ii  libxdamage1               1:1.1.4-2+b1
ii  libxext6                  2:1.3.3-1
ii  libxfixes3                1:5.0.1-2+b2
ii  libxrender1               1:0.9.9-2
ii  libxt6                    1:1.1.5-1
ii  procps                    2:3.3.11-3
ii  zlib1g                    1:1.2.8.dfsg-2+b1

Versions of packages firefox recommends:
ii  gstreamer1.0-libav         1.6.3-1
ii  gstreamer1.0-plugins-good  1.6.3-1

Versions of packages firefox suggests:
ii  fonts-lmodern          2.004.5-1
pn  fonts-stix | otf-stix  <none>
ii  libcanberra0           0.30-2.1
ii  libgnomeui-0           2.24.5-3.1
ii  libgssapi-krb5-2       1.13.2+dfsg-5
pn  mozplugger             <none>

-- no debconf information