The title of the above Wikisource post is misleading. The overall toolbar appears but the 'Proofread tools' part doesn't appear on the first try. The problem is persistent and someone else seconded the issue. I also assembled an over/under screen image here: https://en.wikisource.org/wiki/File:Missing_a_toolbar_which_closes_the_header.jpg (again referring to the Proofreading tools on the toolbar).
Please accept my my apologies. It's called the 'Enable enhanced editing toolbar' option and it's selectable on the user's Preferences\Editing page. I am using the vector skin. The toolbar appears when opening a page for editing in the Page: namespace. About half of the time, the Proofreading tools segment is missing. I can activate it by re-clicking the 'edit' tab as the page is already open for editing. This problem appeared after the latest 1.27.0-wmf.1 (rMWc6068783962b) 06:32, 1 October 2015 update. I hope this helps.
In Xubuntu 14.04 I opened about 10 pages in sequence in edit mode and it was OK.
In Windows, I disabled the MS antivirus, rebooted and it didn't make a difference. The problem is the same.
George Orwell III has placed some code a long time ago in my common.js to mask the unwanted buttons. It never gave me problems and it's used by a number of other editors. Perhaps someone should take a look at the code? https://en.wikisource.org/wiki/User:Ineuw/common.js
It is less likely to be the 'hiding' as that would hide the items after
they have been identified on the sub-toolbar. It is the sub-toolbar
component itself that is missing.
As the sub-part shows in your Ubuntu, it is there, though it sounds like
the rendering of the subpart occurs after the rendering of the whole in
Windows config. <shrug>
Other tests are
- try other browsers in your W/sys to see if it replicates
- get someone with W & Ff & vector to see if they can replicate
I am using Windows at this moment and tested Chrome and Opera extensively. It works fine in bot browsers, so the problem seems to be with Firefox. Another user has this issue intermittently and will ask what browser he's using. We are both able to work and I will continue to probe the issue. Could this be cause by a Firefox extension (addon)?
I don't know as I did not write your Firefox extensions/addons. :)
Does the problem still happen if you start Firefox in Safe Mode? See http://support.mozilla.com/en-US/kb/Safe+Mode
Does this also happen with a new and empty profile? See http://support.mozilla.com/en-US/kb/Basic%20Troubleshooting#w_8-make-a-new-profile and http://support.mozilla.org/kb/Managing%20profiles
Think I found the solution.
It seems to be the enhanced editor code in my common.js. I removed it and ever since then there is no problems. As I look at the current version of the enhanced editor toolbar, the layout is a bit different than it was when George Orwell III wrote the code. If this is so, then his code masked any changes introduced, and we wouldn't have known about it.