Could you explain in more detail what is going wrong? I'll take 3 guesses:

(1) If you are getting frequent popups regarding your video player: These may be from infected sites or from an infection on your system, with an add-on as a common vector of attack.

Here's my suggested procedure for tracking down and cleaning up unwanted add-ons. I know it seems long, but it's not that bad.

(A) Open the Windows Control Panel, Uninstall a Program. After the list loads, click the "Installed on" column heading to group the infections, I mean, additions, by date. This can help in smoking out undisclosed bundle items that snuck in with some software you agreed to install. Be suspicious of everything you do not recognize/remember, as malware often uses important or innocent sounding names to discourage you from removing it. Take out as much trash as possible here.

(B) Open Firefox's Add-ons page using either:

• Ctrl+Shift+a
• "3-bar" menu button (or Tools menu) > Add-ons
• in the Windows "Run" dialog, type or paste
  firefox.exe "about:addons"

In the left column, click Plugins. Set nonessential and unrecognized plugins to "Never Activate".

In the left column, click Extensions. Then, if in doubt, disable (or Remove, if possible) unrecognized and unwanted extensions. Bear in mind that all extensions are optional, none come with Firefox.

Often a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

Any improvement?

If you have more than 15 minutes:

(C) You can search for remaining issues with the scanning/cleaning tools listed in our support article: Troubleshoot Firefox issues caused by malware. These on-demand scanners are free and take considerable time to run. If they finish quickly and especially if they require payment, you may have a serious infection. I suggest the specialized forums listed in the article in that case.

Success?

(2) If Firefox is crashing: Sorry to hear about the crashes. Are you getting the Mozilla Crash Reporter dialog, or the Windows crash dialog? If you are getting the Mozilla Crash Reporter form, your Firefox may have logged some data that would help track down the cause of the problem. You can submit that data to Mozilla and share it with forum volunteers to see whether it points to the solution. Please check the last section of the support article "Firefox Crashes" for steps to get those crash IDs from the about:crashes page, and then post some of the recent ones here.

(3) If you are getting incessant unresponsive script errors: These can be caused by the protected mode feature of the Flash player plugin. That feature has security benefits, but seems to have serious compatibility issues on some systems. There is a hidden setting to disable it; I suggest trying this for a day to see whether it helps:

(A) In a new tab, type or paste about:config in the address bar and press Enter. Click the button promising to be careful.

(B) In the search box above the list, type or paste flash and pause while the list is filtered

(C) Double-click the dom.ipc.plugins.flash.disable-protected-mode preference to switch its value from false to true.

This might not take effect until all Flash has been unloaded for a few minutes, or you close Firefox.

But speaking of out-of-date software, I suggest updating your Adobe Acrobat plugin as follows:

(1) Open Adobe Reader and use Help > Check for Updates to get the latest in the "X" series. This will automatically update Firefox.

(2) Remove obsolete duplicative DLL files. Your Question Details > More System Details shows two versions. To discover the location of the old DLL on disk and remove it, you can type or paste about:plugins in the address bar. Search in the page for nppdf and look for the 10.1.2 version and the path should be listed there.