• The action calls will be processed 'synchronous' now, there is no 'queuing' anymore. E.g. when calling code from an event or from external Javascript it will be processed immediately. This solves many 'ordering' problems and opens many possibilities for faster internal processing.
  
• Due the new synchronous processing, the actions are processed faster now - especially the for() and loop() actions (their inner-loop code will be cached and can be executed way faster).
  
• Improved layouting performance.
  
• Improved WebGL rendering performance.
  
• All kind of image- and videos-hotspots will be rendered by WebGL by default now (and are available for VR/stereo rendering). Textfield- and polygonal-hotspots for WebGL are still in work.
  
• Improved WebVR support - all current WebVR API versions are supported, the older ones and the new WebVR API 1.0, the new GearVR browser is directly support, special support for Firefox (which currently has an older and buggy WebVR rendering resolution support), orientation lock support, more mobile devices.
  
• Direct fisheye image/video support in the viewer.
  
• Direct MJPEG video streaming support (e.g. for dome-webcams).
  
• Stereo hotspots (different images for left/right, via cropping).
  
• Improved videoplayer plugin.
  
• New actions and new settings.
  
• Improved dragging control.
  
• The krpano HTML5 Viewer will be used by default now.
  
• The krpano Embedding Script and krpano HTML5 Viewer are now always merged into one file.
  
• The krpano Testing Server provides an automatically redirecting of local started html files.
  
• Updated tour skin - better VR support, integrated pano-video player.
  
• A completely new videopano skin with VR support - example.
  Included in the download package and easy to use with own videos.
  
• Many many many fixes and detail improvements.
  
• Updated examples.
  

• Textfield hotspots for WebGL/VR
  
• Polygonal hotspots for WebGL/VR
  
• Updated soundinterface plugin
  
• Improved tools (an interface for directly inputting stereoscopic-images and videos)
  
• Some smaller known-issues.
  

• <layer> elements without align setting were positioned wrong
• When changing the crop setting, the width and height settings were not updated instantly like in previous versions.
• In some cases the width and height settings were not set/updated already in the onloaded event and this was leading to many incompatibly problems.
• The position of non-zoomed/non-distorted webgl-hotspots was wrong.
• The size of non-zoomed/non-distorted webgl-hotspots was wrongly 'stage-scaled'.
  
• The position of css3d-hotspots with children elements was wrong in some cases.
• The position of textfield-hotspots was wrong sometimes in some cases.
  
• It was not possible to re-use a videoplayer plugin a second time as pano.
• Don't trigger the onout event when changing/reloading a webgl-hotspot image.
• WebGL creation error when the pano-element had a size of exactly 320x240px at startup.
• Support the latest GearVR 'Samsung Internet' browser.
• Disable/block autorotate in VR mode.
  
• Support HTTPS in Bing Maps plugin.
• The width of an opened combobox was wrong in some cases.
• The name of <action> elements with protect=true were wrongly case-sensitive.
• The defaultskin.xml supports mobilescale=1.0.
• Fixed for the vtourskin.xml: map spots were behind the map in some browsers, calling skin_hideskin at startup works now, improved deep-linking.
• Updated Three.js example.
  

• The lookat() action has now internal WebVR support.
  
• Allow changing the view of the current pano while keeping the view-movement of the old pano during blending (for seamless blending and view-changes in VR mode).
  
• The crop setting wasn't working in some cases (depending on the order of usage).
  
• Rendering/blending bug when using NOBLEND (report).
  
• Invisible hotspots when using NOBLEND.
  
• Avoid rendering mirrored non-distorted hotspots on extreme fisheye distortions.
  
• Workarounds for iPhone 6+ fullscreen landscape mode.
  
• The contextmenu fontsize was too large on HiDPI Windows systems in some browsers (browser bug).
  
• Hiding the DOM element of the krpano HTML5 viewer no longer causes onviewchange event calls (report).
  
• No JS-error when unloading the viewer during WebVR mode.
  
• Updated vtourskin.xml for improved VR support.
  
• vtourskin.xml - new optional linkedscene_lookat="hlookat, vlookat, fov" setting for skin_hotspotstyle-based hotspots to set the startup-view of the linked scene (works also in VR mode and when using the gyro-control).
  
• New debug(), warning(), error() and fatalerror() actions (feature request).
  
• New autorotate.interruptionevents setting to control which events will interrupt the auto-rotation.
  
• Don't stop nexttick/delayedcall actions from an removed element (report). Instead only remove the caller object.
  
• Don't capture the MacOSX system keys (report).
  
• Allow using view.style in Flash (report).
  
• In the subtxt() action the default length parameter wasn't working in Flash (report).
  
• Set failIfMajorPerformanceCaveat to false by default.
  
• Improved resetsensor action in the webvr.js and gyro2.js plugins.
  
• gyro2.js - new softstart setting for slowing fading to the gyro-tracked-position (feature request).
  
• videoplayer.js - support iOS 8 again (report).
  
• webvr.js - new headtracking setting to disable the head-tracking.
  
• webvr.js - avoid unintended mouse-movement when switching to fullscreen mode.
  
• googlemaps.js - key setting for setting the Google Maps API Key (report). The tour.xml/vtourskin.xml were also updated to allow setting the key.
  
• The editor.swf was sometimes saving UTF8 files wrongly.
  
• The protect command line tool can use the 'merged' krpano.js as base file now.
  
• The MAKE OBJET droplet wasn't working in the previous release.
  

Quoted from "requiem434"

Why 1.19.pr4 viewer show this tips at Localbrowsing?
Local usage with file:// urls is limited due browser security restrictions!