Iceweasel runs flawlessly fine in safe mode, but after refresh the browser, it doesn't appear and the message in the terminal is the following:

JavaScript error: resource://gre/modules/AutoCompletePopup.jsm, line 113: NS_ERROR_ILLEGAL_VALUE: Component returned failure code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE) [nsIObserverService.removeObserver]
1575166360853    addons.webextension.screenshots@mozilla.org    WARN    Loading extension 'screenshots@mozilla.org': Reading manifest: Invalid extension permission: mozillaAddons
1575166360853    addons.webextension.screenshots@mozilla.org    WARN    Loading extension 'screenshots@mozilla.org': Reading manifest: Invalid extension permission: telemetry
1575166360853    addons.webextension.screenshots@mozilla.org    WARN    Loading extension 'screenshots@mozilla.org': Reading manifest: Invalid extension permission: resource://pdf.js/
1575166360853    addons.webextension.screenshots@mozilla.org    WARN    Loading extension 'screenshots@mozilla.org': Reading manifest: Invalid extension permission: about:reader*
1575166361285    Marionette    FATAL    Error de análisis XML: entidad indefinida
Ubicación: chrome://browser/content/browser.xhtml
Línea 1918, columna 9:        <toolbaritem id="appMenu-fxa-status" 
--------^
JavaScript error: resource:///modules/BrowserGlue.jsm, line 1836: NS_ERROR_FAILURE: Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIIdleService.removeIdleObserver]
JavaScript error: , line 0: UnknownError: The operation failed for reasons unrelated to the database itself and not covered by any other error code.
JavaScript error: resource://services-common/kinto-offline-client.js, line 603: Error: IndexedDB getLastModified() The operation failed for reasons unrelated to the database itself and not covered by any other error code.

1575166474824    Marionette    FATAL    Error de análisis XML: entidad indefinida
Ubicación: chrome://browser/content/browser.xhtml
Línea 1918, columna 9:        <toolbaritem id="appMenu-fxa-status" 
--------^
JavaScript error: resource://gre/modules/AutoCompletePopup.jsm, line 113: NS_ERROR_ILLEGAL_VALUE: Component returned failure code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE) [nsIObserverService.removeObserver]
JavaScript error: resource://services-common/kinto-offline-client.js, line 603: Error: IndexedDB getLastModified() The operation failed for reasons unrelated to the database itself and not covered by any other error code.

we could not reproduce that error

does the program run when launched with `iceweasel --safe-mode`?
does the program run when launched from a .desktop icon?
do you have 'iceweasel-hardened-preferences' installed?
do you have any additional add-on installed? - you could try disabling them

it is likely you could fix the problem by deleting your user profile directory

$ rm -rf ~/.mozilla/firefox/*.profile/

that will reset any customizations you have made though

or use a bigger hamer and delete the entire mozilla directory:

$ rm -rf ~/.mozilla/

which will reset any customizations you have made in any mozilla program, icedove, icecat, etc

After wipe out my .mozilla folder, the result gets worse:

JavaScript error: resource://gre/modules/AutoCompletePopup.jsm, line 113: NS_ERROR_ILLEGAL_VALUE: Component returned failure code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE) [nsIObserverService.removeObserver]
JavaScript error: resource://gre/modules/AsyncShutdown.jsm, line 694: Error: Phase "profile-before-change" is finished, it is too late to register completion condition "JSON store: writing data" 
JavaScript error: resource://services-common/kinto-offline-client.js, line 603: Error: IndexedDB getLastModified() The operation failed for reasons unrelated to the database itself and not covered by any other error code.

Result of Iceweasel running with firejail:

Reading profile /etc/firejail/iceweasel.profile
Reading profile /etc/firejail/firefox.profile
Reading profile /etc/firejail/firefox-common.profile
Reading profile /etc/firejail/disable-common.inc
Reading profile /etc/firejail/disable-devel.inc
Reading profile /etc/firejail/disable-exec.inc
Reading profile /etc/firejail/disable-interpreters.inc
Reading profile /etc/firejail/disable-programs.inc
Reading profile /etc/firejail/whitelist-common.inc
Reading profile /etc/firejail/whitelist-var-common.inc
Parent pid 6376, child pid 6377
Warning: An abstract unix socket for session D-BUS might still be available. Use --net or remove unix from --protocol set.
Warning: /sbin directory link was not blacklisted
Warning: /usr/sbin directory link was not blacklisted
Post-exec seccomp protector enabled
Seccomp list in: @clock,@cpu-emulation,@debug,@module,@obsolete,@raw-io,@reboot,@resources,@swap,acct,add_key,bpf,fanotify_init,io_cancel,io_destroy,io_getevents,io_setup,io_submit,ioprio_set,kcmp,keyctl,mount,name_to_handle_at,nfsservctl,ni_syscall,open_by_handle_at,personality,pivot_root,process_vm_readv,ptrace,remap_file_pages,request_key,setdomainname,sethostname,syslog,umount,umount2,userfaultfd,vhangup,vmsplice, check list: @default-keep, prelist: adjtimex,clock_adjtime,clock_settime,settimeofday,modify_ldt,lookup_dcookie,perf_event_open,process_vm_writev,delete_module,finit_module,init_module,_sysctl,afs_syscall,create_module,get_kernel_syms,getpmsg,putpmsg,query_module,security,sysfs,tuxcall,uselib,ustat,vserver,ioperm,iopl,kexec_load,kexec_file_load,reboot,set_mempolicy,migrate_pages,move_pages,mbind,swapon,swapoff,acct,add_key,bpf,fanotify_init,io_cancel,io_destroy,io_getevents,io_setup,io_submit,ioprio_set,kcmp,keyctl,mount,name_to_handle_at,nfsservctl,open_by_handle_at,personality,pivot_root,process_vm_readv,ptrace,remap_file_pages,request_key,setdomainname,sethostname,syslog,umount2,userfaultfd,vhangup,vmsplice,
Warning: Cannot confine the application using AppArmor.
Maybe firejail-default AppArmor profile is not loaded into the kernel.
As root, run "aa-enforce firejail-default" to load it.
Child process initialized in 183.15 ms
1575167890830    addons.webextension.screenshots@mozilla.org    WARN    Loading extension 'screenshots@mozilla.org': Reading manifest: Invalid extension permission: mozillaAddons
1575167890830    addons.webextension.screenshots@mozilla.org    WARN    Loading extension 'screenshots@mozilla.org': Reading manifest: Invalid extension permission: telemetry
1575167890830    addons.webextension.screenshots@mozilla.org    WARN    Loading extension 'screenshots@mozilla.org': Reading manifest: Invalid extension permission: resource://pdf.js/
1575167890830    addons.webextension.screenshots@mozilla.org    WARN    Loading extension 'screenshots@mozilla.org': Reading manifest: Invalid extension permission: about:reader*
1575167891522    Marionette    FATAL    Error de análisis XML: entidad indefinida
Ubicación: chrome://browser/content/browser.xhtml
Línea 1918, columna 9:        <toolbaritem id="appMenu-fxa-status" 
--------^
JavaScript error: resource://gre/modules/AutoCompletePopup.jsm, line 113: NS_ERROR_ILLEGAL_VALUE: Component returned failure code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE) [nsIObserverService.removeObserver]

Parent is shutting down, bye...

[eliotime3000@ELTM3K ~]$ iceweasel --new-instance
1575168164588    Marionette    FATAL    Error de análisis XML: entidad indefinida
Ubicación: chrome://browser/content/browser.xhtml
Línea 1918, columna 9:        <toolbaritem id="appMenu-fxa-status" 
--------^
JavaScript error: resource://gre/modules/AutoCompletePopup.jsm, line 113: NS_ERROR_ILLEGAL_VALUE: Component returned failure code: 0x80070057 (NS_ERROR_ILLEGAL_VALUE) [nsIObserverService.removeObserver]

OK. I found the cause of the problem.

The main issue was the language pack. I've uninstalled the iceweasel-l10n-es-ar package and the problem has been solved by art of magic. Maybe the rest of language packs could have the same issue, so I'll share this bug report into the troubleshooting related to Iceweasel language pack thread.

Thanks by their comprehension and apologizes by all the suffering.

Now, the error of the Iceweasel language pack has been created in the Bug #2571: [iceweasel-l10n-es-ar][iceweasel-l10n-pl]: Iceweasel doesn't start with some language packs bug report. Any comment related with the error reported here with the iceweasel-l10n-es-ar language pack must on the bug report quoted previously.

The error message looks like the one I mentioned earlier in [1] (see # 6). Perhaps branding files in langpacks should be updated the same way as in that patch.

[1] https://lists.parabola.nu/pipermail/dev/2019-October/007484.html