Not able to reproduce, the editor loads as expected. Could you please add a step by step process for "How to reproduce"?

Anyway, this should not be a Highest level issue:
https://docs.joomla.org/Priority

Thank you and apologies for priority error ( I don't know where to change it at the minute, will do when I've found that)
Step by step process:
1. I go to http://future-is-now.net/administrator/index.php,
2. log in with my usual super user credentials
3. go to extensions and then modules
4. select type "custom"
5. open an existing module
The module appears in source code mode, can be toggled, though. The normal menu (module, menu assignment, module permissions etc.) is not appearing and none of the buttons (save, save and close etc) are working. The module cannot be closed.

I have cleared the joomla cache, browser cache, tried a different browser but the problem persists. I have got another joomla site with still 3.4.8 running and there the modules work fine.

i have changed the priority for you ;)

This sounds like a failed update

On 24 March 2016 at 13:09, Brian Teeman brian@teeman.net wrote:

i have changed the priority for you ;)

Brian Teeman
Co-founder Joomla! and OpenSourceMatters Inc.
http://brian.teeman.net/

Same problem with articles. what next?

What wysiwyg editor do you have installed or is it just the default

Just default.
From: Brian Teeman
Sent: Thursday, March 24, 2016 2:38 PM
To: joomla/joomla-cms
Cc: meninaisabella
Subject: Re: [joomla-cms] Update to joomla 3.5 - custom modules - pages freeze (#9567)

What wysiwyg editor do you have installed or is it just the default

This comment was created with the J!Tracker Application at issues.joomla.org/joomla-cms/9567.
—
You are receiving this because you authored the thread.
Reply to this email directly or view it on GitHub

just default

So I would guess that there is a third party content plugin that is
misbehaving or a faulty update
Go to your plugin manager and try to disable any content plugins that you
have installed and see if that fixes it

It's the TinyMCE that's not working and blocking things. When I switch it off, the tabs appear again and the buttons work.

OK we are getting close. Do you have any editor plugins? Try disabling them

There are only the three that come with Joomla. CodeMirror, None, and TinyMCE. Do you want me to disable all of them?

I am not talking about those. I am taking about the plugins in this group
editors-xtd

That's it! I've disabled all of them and the editor is working again. The rest I can figure out myself I think, finding out which one causes the problem. Brilliant, thank you so much!!

Great - I am closing this now - if it turns out to be one of the core plugins please post back but I am sure it wont be

No, it's not, it's the POWr Icon one, for the facebook feed. Thanks again!