I am able to crash a debug build by using target="_blank" in a tags. A normal build just stops working and kills extensions. There is no useful output on the console, even in debug builds.

STR:

1. Install add-on
2. Click on CLICK button in main toolbar
3. You see 3 links. The first one works, the second one does not, the third on kills TB (debug build)
4. After clicking on the second link, the add-on as basically dead (clicking on the CLICK button is not opening the page any more) and the add-on has to be disabled/enabled first.

Depends on D167045

Try analysis

Without this patch:
https://treeherder.mozilla.org/jobs?repo=try-comm-central&revision=dd9a11a4e4244483ecadce4927bb03f43adaa602
With this patch:
https://treeherder.mozilla.org/jobs?repo=try-comm-central&revision=a296a67d6ef884e5501c1cffad24e62b8d4b3cf7

Additional fails on first run:

Linux opt:
X3: toolkit/components/extensions/test/xpcshell/test_ext_contentscript_errors.js
bct3: comm/mail/components/addrbook/test/browser/browser_edit_card.js
bct3: comm/mail/components/addrbook/test/browser/browser_edit_photo.j

Linux debug:
bct2: comm/mail/base/test/browser/browser_formPickers.js
bct2: comm/mail/base/test/browser/browser_linkHandler.js
bct3: Assertion failure: mDocGroup->GetBrowsingContextGroup() == GetBrowsingContext()->Group(), at /builds/worker/checkouts/gecko/dom/base/Document.cpp:4260
bct3: comm/mail/components/addrbook/test/browser/browser_contact_tree.js
bct5: comm/mail/test/browser/attachment/browser_attachmentMenus.js
bct7: Assertion failure: mDocGroup->GetBrowsingContextGroup() == GetBrowsingContext()->Group(), at /builds/worker/checkouts/gecko/dom/base/Document.cpp:4260

OSX opt:
bct7: comm/mail/test/browser/tabmail/browser_dragndrop.js

OSX debug:
bct5: comm/mail/test/browser/attachment/browser_attachmentMenus.js

Win opt:
X1: toolkit/components/downloads/test/unit/test_DownloadLegacy.js
X4: toolkit/components/cleardata/tests/unit/test_network_cache.js

Win debug:
bct1: ?
bct5: comm/mail/test/browser/attachment/browser_openAttachment.js

Win 64 debug:
X2: toolkit/components/antitracking/test/xpcshell/test_staticPartition_prefetch.js

The failed tests succeeded on second run. Win 32 debug bct1 log file however cannot be parsed (in both try runs).

Pushed by mkmelin@iki.fi:
https://hg.mozilla.org/comm-central/rev/b6f7d07e544b
Fix target links for WebExtensions. r=darktrojan

This is still crashing debug builds:
https://treeherder.mozilla.org/jobs?repo=try-comm-central&revision=00f794fef7c0f65f0c535b215cb072ebe3395693&selectedTaskRun=N9LuHz26R7OKpDYN3AWhgA.0

Removing the check from the test (to get rid of the test fail) and re-opening this to fix the debug crash.

Pushed by mkmelin@iki.fi:
https://hg.mozilla.org/comm-central/rev/0b8daf815bf2
Disable clickhandler test for debug builds, but run all parts for non-debug builds. r=mkmelin