When I click on "back" button using version 26 it doesn't take me back where I was , but back two steps, like I clicked "back" twice.
hello, can you try to replicate this behaviour when you launch firefox in safe mode once? if not, maybe an addon is interfering here...
Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems
There are other things that need your attention.
Please update to the current Firefox 26 release.
The Firefox 25.0.1 version that you currently run is no longer supported with security updates.
Note that your System Details List shows multiple outdated Flash plugins.
You can find the installation path of all plugins on the aboutlugins page.
You can check the Flash player installation folder for multiple Flash player plugins and remove all (older) version(s) of the plugin (NPSWF32) and (re)install the latest Flash player.
Latest Flash player versions here: