this video show you if your firefox coninuously hangs up and then how you can set that.
Open your profile folder:

Click the menu button New Fx Menu , click help Help-29 and select Troubleshooting Information. The Troubleshooting Information tab will open.
Under the Application Basics section, click on Show Folder. A window with your profile files will open.
Click the menu button New Fx Menu and then click Exit Close
Wait until Firefox has completely quit.
In the Firefox profile folder, find and rename the files places.sqlite to places.sqlite.old
To rename a file, right-click on it and select rename from the menu. Then add .old to the end of its name.
Finally, reopen Firefox.
When Firefox reopens it will create a new places database. Your browsing history will be lost but Firefox will automatically import your bookmarks from the most recent backup file.

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