Crashes when opening certain dialogs

1. Go to Settings: Web browser
2. Change the URL of the home page and save

I briefly see a prompt to restart and then Steam crashes. This happens for every dialog that triggers this prompt.

1. Start any game running on Proton

There is a Steam-dialog opening saying something about FAQs and then Steam crashes the same way as it does for other Steam-dialogs.

Install dialogs work fine. Other dialogs work fine. These two types of dialogs seemto trigger a crash.

GameAction [AppID 298610, ActionID 1] : LaunchApp changed task to ShowSteamPlayWarning with ""
GameAction [AppID 298610, ActionID 1] : LaunchApp waiting for user response to ShowSteamPlayWarning ""
Failed to open digital audio driver No mixer services exist.
crash_20181129165022_1.dmp[320]: Uploading dump (out-of-process)
/tmp/dumps/crash_20181129165022_1.dmp
/home/user/.var/app/com.valvesoftware.Steam/.local/share/Steam/steam.sh: line 889: 126 Segmentation fault (core dumped) $STEAM_DEBUGGER "$STEAMROOT/$STEAMEXEPATH" "$@"
crash_20181129165022_1.dmp[320]: Finished uploading minidump (out-of-process): success = yes
crash_20181129165022_1.dmp[320]: response: CrashID=bp-8548e907-128c-47e6-b1a6-xxxxxxxxxxxxx
crash_20181129165022_1.dmp[320]: file ''/tmp/dumps/crash_20181129165022_1.dmp'', upload yes: ''CrashID=bp-8548e907-128c-47e6-b1a6-xxxxxxxxxxxxx''

Fedora 29