So, we all know HTML panel is screwed over by being stuck with the IE7 rendering engine, right?
Not any more
It turns out you can control what HTML rendering engine a given Windows app uses via the registry. (Tested on Windows 10)
(Instructions adapted from here):
There are one or two keys you have to add to, depending on if you use a 64 bit or 32 bit machine. I used both:
32 bit only or 64 bit:
Go to: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_BROWSER_EMULATION
Make a new 32 bit DWORD Value, name it xwidget.exe
Right click in the Data column of that value and make a Decimal value of 9999
(This makes xwidget use the IE9 renderer, I dunno the codes for 10 or 11 yet)
Then go to
HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\Internet Explorer\MAIN\FeatureControl\FEATURE_BROWSER_EMULATION
And repeat the process. This key may not be there on 32 bit systems and that's fine you can skip the step.
No reboot is needed. Restart Xwidget and BAM! It runs the IE9 renderer.
EDIT: The code for IE 11 / Edge is 11001 and I can confirm it works. (taken from here).
If Tony ever updates the app, adding those keys in to the registry at at least 9999 should really improve things.