Firefox alt-left alt-right not working

Few days ago I noticed that my Firefox alt-left, alt-right keyboard shortcuts are not working anymore.. As I am using the keyboard extensively especially those 2 hotkeys and I was very annoyed by this problem. I was sure that this trouble was generated by one of my many extensions. Due to the large number of extensions installed disbaling them one by one was not a practical sollution. So I checked all with KeyConfig and found a bug in DuplicateTab extension. I like this extension because it can clone the browser history to the new tab along with the url so I checked the extesion and searched for an update but Firefox said one was not available.. I then went to extension's page and found out that there is an update indeed.. Installed it and everythings got back to normal.. Pretty weird that Firefox's extension manager didnt noticed me about the update.

DAP could not be loaded. Please press "back" button on the browser.

I used to install DAP to be used with firefox as download accelerator but after few days of testing I didnt liked its behaviour and decided to uninstall it. Somehow, it seems that Download Accelarator Plus doesnt like to be unistalled so he decided the firefox extension will be still useful to me. When I try to download something with firefox I get a pop-up info window saying:
"DAP could not be loaded. Please press "back"
button on the browser."
When I press OK a gray screen appears with the message:
"Download Accelerator has added the link to queues.
Press "Back" button to return to normal mode"
This aborts the download.

Somehow this stupid plugin doesnt remove itself from firefox and annoys me big times. I tried re-installing and the same thing happens. After some google search I found out that many people are annoyed by this stupid error so I decided to install it on another computer and monitor the instalation changes made by the both the installer and uninstaller.

I found out that DAP doesnt remove all the files it installs. It forgot some dll in Firefox installation directory. If you want to get rid of it you just have to go into Firefox install directory then you'll fins a directory named plugins. In this directory search and remove the file named npdap.dll and you're done!