I see that Sharky has presented the best/correct solution, but I'd like to take a moment to build a bit of understanding around this occurrence.
For the record, date is a MYSQL Keyword, but not a Reserved Keyword, so no quoteName() calls are necessary.
First, what is the query that your script is generating...
WHERE 'date ...
Yes, disable all unused components
In the Joomla back-end via Extensions > Manage > Manage
click [Search Tools] button and select:
Unprotected + Administrator + Component
Select all unused components (probably banners, contacts, newsfeeds) and click "disable".
Do not uninstall, just disable them.
Most form views in core components have custom Joomla.submitbutton() functions. Standard function does indeed support only adminForm as form ID. Instead you can use Joomla.submitform() and pass your form:
<button class="btn btn-primary" type="button" onclick="Joomla.submitform('controller.send', this.form)" >Send</button>
Assuming you're using the Form API, add buttons="true" attribute to your editor field. Example from article form:
I did manage to solve it in the end, although I still have no idea why the inline code - which was added by Firefox, not me - was added.
I compared the html/css class code for the menu with another menu that wasn't doing the same thing. This code was faulty:
<?php if ($this->countModules('mainmenu')) : ?>
You have to create a router for your component for JRoute::_() to do anything. See Supporting SEF URLs in your component documentation. I suggest looking specifically at Simple View-based Example which uses a new way of working with routing.