For some odd reason AdBlock Plus in Firefox choose to use the keyboard CTRL+SHIFT+V to open the sidebar (blockable items). The problem with using this is CTRL+SHIFT+V is the universal keyboard shortcut to Paste as Plain Text of Paste without Formatting. After some searching I found a thread from October 2012 on the Adblock Plus Forums that provided a solution:

• In a new tab type about:config and press enter
• If needed click the I’ll be careful, I promise button on the ‘This might void your warranty warning’.
• In the search box paste extensions.adblockplus.sidebar_key
• You should see one result as a string with the default value of Accel Shift V, Accel Shift U (note: Accel is Control on Windows/Linux and Command on OS X).
• Double-click on the entry to edit. Delete Accel Shift V, so only Accel Shift U is the value
• Click OK to save then close the tab
• Changes take effect as soon as you restart Firefox

What I don’t understand is why they had two shortcuts for the same function and why they would use one that is a universal keyboard shortcut. This also applies to AdBlock Plus within Thunderbird.