Block editing disappeared Until last week, when i logged in as administrator, on the page of nodes,
i could edit blocks by clicking "edit this block" link which appeared in upper right corner of blocks.
But now i can't see edit block link, so for every time i want to edit block i go to "/admin/structure/block" which is very bad.

When i check the page source i can see the links like:

&lt;div class="contextual-links-wrapper"&gt;
&lt;ul class="contextual-links element-hidden"&gt;
&lt;li class="block-configure first last"&gt;   
&lt;a href="/admin/structure/block/manage/block/32/configure?  
destination=admin/config/development/performance"&gt;Edit block&lt;/a&gt;&lt;/li&gt;
&lt;/ul&gt;&lt;/div&gt;


What would be the problem.
How can i solve this?
Can you please help me.
Do you have the Theme Developer module enabled? I had the same problem (disappearing contextual links menu for blocks) and disabling the Theme Developer module resolved the issue. Likely something to do with the z-order being utilized by Theme Developer.