[Xposed Framework Modules] defkev:
Upload a logcat of org.mozilla.firefox (or whatever package you are using) and i'll take a look.

04-02 21:29:38.344 E/GeckoCrashHandler(8609): >>> REPORTING UNCAUGHT EXCEPTION FROM THREAD 1 ("main")
04-02 21:29:38.344 E/GeckoCrashHandler(8609): java.lang.NullPointerException: Attempt to invoke interface method 'boolean org.mozilla.gecko.text.TextSelection.dismiss()' on a null object reference
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at org.mozilla.gecko.BrowserApp$3.onInterceptTouchEvent(BrowserApp.java:655)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at org.mozilla.gecko.toolbar.BrowserToolbar.onInterceptTouchEvent(BrowserToolbar.java:968)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2175)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2604)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2321)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2604)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2321)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2604)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2321)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2604)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2321)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2604)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2321)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2604)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2321)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2604)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2321)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2604)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:2321)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchTransformedTouchEvent(ViewGroup.java:2604)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.cancelAndClearTouchTargets(ViewGroup.java:2454)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewGroup.dispatchDetachedFromWindow(ViewGroup.java:3162)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewRootImpl.dispatchDetachedFromWindow(ViewRootImpl.java:3307)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewRootImpl.doDie(ViewRootImpl.java:6020)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.ViewRootImpl.die(ViewRootImpl.java:5997)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.WindowManagerGlobal.removeViewLocked(WindowManagerGlobal.java:486)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.WindowManagerGlobal.removeView(WindowManagerGlobal.java:424)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.view.WindowManagerImpl.removeViewImmediate(WindowManagerImpl.java:126)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:4333)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4585)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.app.ActivityThread.-wrap19(ActivityThread.java)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1531)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.os.Handler.dispatchMessage(Handler.java:102)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.os.Looper.loop(Looper.java:163)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at android.app.ActivityThread.main(ActivityThread.java:6238)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at java.lang.reflect.Method.invoke(Native Method)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:933)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:823)
04-02 21:29:38.344 E/GeckoCrashHandler(8609):	at de.robv.android.xposed.XposedBridge.main(XposedBridge.java:107)

I suppose there isn't enough space to draw the toolbar.

Try lowering the DPI and/or disable the Full actionbar.