not sure what you mean by "does not show icon" but Firefox changed the download manager API in FF 26 so have a look here and see if this info helps any
http://www.ghacks.net/2013/12/14/firefox-26-broken-download-extensions-left-right/
Firefox 26: broken download extensions left and right
By Martin Brinkmann on December 14, 2013 in Firefox
Firefox 26 has been out for some days now, a rather unspectacular update for many users as it does not really ship with that many new or improved features
One of the changes in Firefox 26 that I did not mention in the review is the removal of the old download manager API.
Mozilla did introduce a new download manager API in Firefox 20 to resolve performance issues of the old, but did not remove the old API immediately.While the new download panel was the default way that downloads were handled in Firefox 20 and newer, there was still a way for users to use the old download manager interface instead.
The old download manager opened in a window instead of in a panel inside the browser window. Firefox users had to switch the preference browser.download.useToolkitUI in about:config to true to use the old API instead of the new one.
The option to do so was removed in Firefox 26, leaving some users puzzled in the process.
Firefox 26: Find out what is new
http://www.ghacks.net/2013/12/10/firefox-26-find-new/
"Lots of changes to interfaces, APIs and DOM"
do you mean you can not download with Firefox or is it that the download part looks different ?
James