There is a bug in Firefox 40 regarding <select> and <option> but I'm not sure it's relevant to your case.

By the way, If you are a system administrator, it is recommended to deploy Firefox 38 ESR instead of the latest Release version.

If you tab to the select control, optionally use Alt+down arrow to drop the list open, use the down arrow key to select the desired option, and then press Enter or tab out of the control, does that work?

Or in other words, can we say this is a problem with how your Firefox is handling mouse events...

Hi JSCHER2000

I did edit my original post, but it seemed to have created another post you can use the arrows and enter, but it doesn't recognize the mouse click on select

Just updated to 40.0.2 in our office and all machines cannot select from drop down boxes. Clicking the box activates the drop down, but the selection will not select, although it can be selected by hitting "enter" on keyboard

The ESR wouldn't work as i need to have the most up to date browser like my customers as we build and design recruitment websites,.

Are there any sites or demo pages online that exhibit this problem that you could provide a link to?

unfortunately not. the issues all stem in the admin areas of sites.

I have had a scan across forums and a few other people have reported it.

its fine in chrome / ie 11 etc and was in version 39

Okay, then I suggest checking for the issue identified by Kohei: https://support.mozilla.org/questions/1077854#answer-768317

HI I have, which will resolve my issue, but not our customers. who think there is something wrong with our sites, when there isn't

I'm not sure what you mean about fixing your Firefox and not your site. This sounds like something that would be a scripting issue on your site:

Regression: <option> cannot be selected in certain circumstances

• Bug 1194733 - [Not e10s] Version 40.0.2 has issue with jquery ibutton plugin

The <option> element cannot be selected and the parent <select> element won't be closed, when Event.preventDefault is called in a mouseup event handler on <select> or its ancestors. The iButton jQuery plug-in is known to be affected. Mozilla developers have identified the cause and are working on a solution.

Source: https://developer.mozilla.org/Firefox/Releases/40/Site_Compatibility#HTML