Hi, a ghost in the machine, please try : SAFE MODE

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

In Firefox Safe mode these changes are effective:

• all extensions are disabled (about:addons)
• default theme is used (no persona)
• userChrome.css and userContent.css are ignored (chrome folder)
• default toolbar layout is used (file: localstore-safe.rdf)
• Javascript JIT compilers are disabled (prefs: javascript.options.*jit)
• hardware acceleration is disabled (Options > Advanced > General)
• plugins are not affected
• preferences are not affected

TEST''''is issue still there ?

This was a good suggestion, but I found that in "safe mode" I was unable to use my current add-ons to try downloading a video. This made it impossible to test to see what add-ons were screwing me up. I resolved the issue, temporarily, by chucking "Video Downloader" and its neccesary accompanying software, and adding a more simplistic tool, which neither offers as many options, nor screws with my tabs. Thanks for the effort!

Do you have the colorful tabs extension?