STEPS TO REPRODUCE
1. download Firefox nightly
https://www.mozilla.org/en-US/firefox/channel/desktop/
2. extract the downloaded archive
3. open the extracted "firefox" folder

OBSERVED RESULT
plasma notifies about kdeint5 crash

EXPECTED RESULT
no crash

SOFTWARE/OS VERSIONS
Operating System: KDE neon Unstable Edition
KDE Plasma Version: 5.18.80
KDE Frameworks Version: 5.70.0
Qt Version: 5.14.1

Application: kdeinit5 (kdeinit5), signal: Segmentation fault
Content of s_kcrashErrorMessage: [Current thread is 1 (Thread 0x7feeba62f780 (LWP 21017))]
[KCrash Handler]
#6  0x00007feeb9ce1003 in XAddExtension (dpy=dpy@entry=0x55d6195e9150) at ../../src/InitExt.c:73
#7  0x00007fee7eea92e5 in _XftDisplayInfoGet (dpy=dpy@entry=0x55d6195e9150, createIfNecessary=createIfNecessary@entry=1) at ../../src/xftdpy.c:91
#8  0x00007fee7eead8de in XftFontInfoFill (dpy=dpy@entry=0x55d6195e9150, pattern=pattern@entry=0x55d619cbee80, fi=fi@entry=0x7ffd8ca131d0) at ../../src/xftfreetype.c:367
#9  0x00007fee7eeae256 in XftFontOpenPattern (dpy=0x55d6195e9150, pattern=pattern@entry=0x55d619cbee80) at ../../src/xftfreetype.c:1015
#10 0x00007fee7f0bcbcf in KFI::CFcEngine::getFont(int) (this=this@entry=0x55d619cca3c8, size=size@entry=8) at ./kcms/kfontinst/lib/FcEngine.cpp:1299
#11 0x00007fee7f0bd1a2 in KFI::CFcEngine::queryFont() (this=this@entry=0x55d619cca3c8) at ./kcms/kfontinst/lib/FcEngine.cpp:1233
#12 0x00007fee7f0bd9e8 in KFI::CFcEngine::getSizes() (this=0x55d619cca3c8) at ./kcms/kfontinst/lib/FcEngine.cpp:1391
#13 0x00007fee7f0bf3f0 in KFI::CFcEngine::draw(QString const&, unsigned int, int, QColor const&, QColor const&, int, int, bool, QList<KFI::CFcEngine::TRange> const&, QList<KFI::CFcEngine::TChar>*) (this=this@entry=0x55d619cca3c8, name=..., style=style@entry=4294967295, faceNo=faceNo@entry=0, txt=..., bgnd=..., w=128, h=128, thumb=true, range=..., chars=0x0) at ./kcms/kfontinst/lib/FcEngine.cpp:876
#14 0x00007fee7f2c6275 in KFI::CFontThumbnail::create(QString const&, int, int, QImage&) (this=0x55d619cca3c0, path=..., width=128, height=128, img=...) at ./kcms/kfontinst/thumbnail/FontThumbnail.cpp:114
#15 0x00007feeaa7e6f24 in ThumbnailProtocol::createSubThumbnail(QImage&, QString const&, int, int) (this=this@entry=0x7ffd8ca13be0, thumbnail=..., filePath=..., segmentWidth=segmentWidth@entry=54, segmentHeight=segmentHeight@entry=34) at ./thumbnail/thumbnail.cpp:727
#16 0x00007feeaa7e7538 in ThumbnailProtocol::drawSubThumbnail(QPainter&, QString const&, int, int, int, int, int) (this=this@entry=0x7ffd8ca13be0, p=..., filePath=..., width=width@entry=54, height=height@entry=34, xPos=xPos@entry=9, yPos=38, frameWidth=2) at ./thumbnail/thumbnail.cpp:759
#17 0x00007feeaa7e7b82 in ThumbnailProtocol::thumbForDirectory(QUrl const&) (this=this@entry=0x7ffd8ca13be0, directory=...) at ./thumbnail/thumbnail.cpp:562
#18 0x00007feeaa7e8fc4 in ThumbnailProtocol::get(QUrl const&) (this=0x7ffd8ca13be0, url=...) at ./thumbnail/thumbnail.cpp:238
#19 0x00007feeb1649b8d in KIO::SlaveBase::dispatch(int, QByteArray const&) (this=0x7ffd8ca13be0, command=67, data=...) at ./src/core/slavebase.cpp:1198
#20 0x00007feeb164a476 in KIO::SlaveBase::dispatchLoop() (this=this@entry=0x7ffd8ca13be0) at ./src/core/slavebase.cpp:338
#21 0x00007feeaa7e6230 in kdemain(int, char**) (argc=<optimized out>, argv=<optimized out>) at ./thumbnail/thumbnail.cpp:138
#22 0x000055d6190683ad in launch(int, char const*, char const*, char const*, int, char const*, bool, char const*, bool, char const*) (argc=4, _name=0x55d6195e1378 "/usr/lib/x86_64-linux-gnu/qt5/plugins/kf5/kio/thumbnail.so", args=<optimized out>, cwd=<optimized out>, envc=0, envs=<optimized out>, reset_env=false, tty=0x0, avoid_loops=false, startup_id_str=0x55d61906ae87 "0") at ./src/kdeinit/kinit.cpp:708
#23 0x000055d6190697cb in handle_launcher_request(int, char const*) (sock=8, who=<optimized out>) at ./src/kdeinit/kinit.cpp:1146
#24 0x000055d61906a05b in handle_requests(pid_t) (waitForPid=0) at ./src/kdeinit/kinit.cpp:1339
#25 0x000055d619065004 in main(int, char**) (argc=3, argv=<optimized out>) at ./src/kdeinit/kinit.cpp:1777