Readingruler

Based on this script:
https://greasyfork.org/en/scripts/372448-reading-ruler/code

This reading ruler will aid you on reading texts on the internet
It will place a semi-transparent line on your screen, just hit the combination ctrl + r on windows and mac (not the command button but the control button) to activate the ruler, hit the same configuration to remove the ruler

This idea come from the reddit user /u/VectorLightning
And the thread can be found here: https://www.reddit.com/r/SomebodyMakeThis/comments/9huwbw/smt_a_firefox_addon_that_adds_a_horizontal/

I hope you find this extension useful

Releases Notes:
V4.1
Bug fixes
- Fixed the keyboard shortcut not working. The root cause was a race condition in the background service worker settings hadn't finished loading from storage when the shortcut was pressed, causing a silent crash that prevented the ruler from ever appearing.
- Fixed the extension not working on tabs that were already open before the extension was installed or updated. The content script is now injected on-demand when needed, so there is no longer a need to reload existing tabs.
- Fixed ruler opacity not saving correctly - the value from the slider was being stored as a string instead of a number.
- Fixed a background script security issue where the message handler could invoke arbitrary functions.

UI
- Redesigned the popup with a clean, minimal layout
- Keyboard shortcuts are now displayed with proper kbd key styling.
- Opacity slider now shows the current value as you drag it.
- Save button gives visual confirmation when settings are saved.
- Removed all external dependencies (Bootstrap, jQuery, Google Fonts, bootstrap-toggle) - the popup no longer requires an internet connection to render correctly and loads instantly.

V4.0
Redo of the extension, all the features introduced on V3.1 were causing a lot of bug, surprisingly there are still people using and finding this extension, so I decided to simplify it and make it work on all websites. I hope this update fixes all major issues reported on the feedback page.

Here a list of changes:
- You are not able to set a shortcut anymore, for now these are set by default.
- Windows: ALT + SHIFT + 3
- Mac: Command + SHIFT + U
- Color and opacity are still options that you can change
- Add save button to apply changes done to the ruler color and opacity
- Fix issue with ruler not working on multiple websites
- Simplified core mechanism to allow extension to always work

V3.1
Lots of improvements, extension should now always work and should not be invisible

- fix problem where ruler would not show on screen (for real this time!)
- new popup layout with 2 new options
- you now can choose a color for your ruler
- you can now set how visible you want your ruler to be
- update core code
- remove itself when its orphaned
- create functions to prevent references on event handlers
- remove unnecessary calls to background script
- overall improve code to work better

v3.0.1
- Avoid exceptions when extension is updated
- Increase z index of ruler to try to push to the foreground

v3.0
- Code rewrite to make extension function properly
- Update manifest to V3
- Fix extension so it should only show the ruler when active
- Drop support for Alt modifier key, you can now only combine CTRL, SHIFT and a keyboard key
- Drop badge text since it was not working anymore

v 2.2
- Fix issue with ruler not showing when pressing the toggle combination

v 2.1
- Add badge to extension icon to let you know the tool is active

v 2.0
- Add options page
- Allow user to choose from using CTRL, ALT and SHIFT plus a key
- Update and rewrite the entire code to be more OOP