We're sorry to hear that your Firefox seems to be crashing when you open it. Please perform the following steps to give us a crash report ID that helps us find out more about the cause of the crash.

1. On the keyboard, press [Windows] The image "Windows key" does not exist. + [R]. This should bring up a Run window that contains a text field.
2. In that text field, type %APPDATA% and press Enter. An explorer window should open.
3. From that explorer window, double-click on the Mozilla folder, then double-click on Firefox and then on Crash reports. Double-click on submitted.
4. Now, you should see a list of files that contain reports. Go to View > Arrange Icons by > Modified to get the most recent files at the top of the window.
5. Open the most recent 5 files with a text editor and copy the IDs.
6. Paste each ID with bp- into the reply window on the forums.

Thanks in advance!

You can find more information and troubleshooting steps in the Troubleshoot Firefox crashes (closing or quitting unexpectedly) article.

Crash ID: bp-64633b8d-a6ac-4982-a6eb-e83aa2150818 Crash ID: bp-e502fa65-dc3f-4385-a5a8-d5cf62150818 Crash ID: bp-569690d8-c014-4dc4-bfac-110cf2150818 Crash ID: bp-90ff08fc-dd83-4968-9f4f-e3fb12150818 Crash ID: bp-d44ed4e4-05f3-44a1-a2c1-5a7b62150818

All 5 crash reports show this. Firefox 39.0.3 Crash Report [@ js::frontend::BytecodeEmitter::maybeEmitVarDecl(JSOp, js::frontend::ParseNode*, unsigned int*) ]

Sorry, I don't understand that type of crash. Another contributor will need to help you.