Mozilla plans to improve the visibility of custom zoom levels in the Firefox web browser starting in version 51 by displaying levels in the address bar.
Firefox’s custom per-page zoom level feature is quite useful. You may use it to increase or decrease the zoom level of any given page to make content smaller or larger.
Introduced in Firefox 3, the feature allows Firefox users to set different zoom levels for domains they visit in the browser.
The zooming functionality changed over the years. Firefox displayed zoom controls in the View menu, and as a button to increase or decrease it. These interface elements are not shown by default anymore, which makes it difficult sometimes to determine the zoom level while looking at a page.
Since it is relatively easy to zoom, by holding down Ctrl and using the mouse wheel or the +/- keys on the keyboard, it may happen occasionally that the zoom level changes unintentionally.
Firefox 51: custom zoom level in address bar
If you run Firefox 51 or newer, you may have noticed the new custom zoom level indicator in the address bar already.
It displays the zoom percentage if it is not the default value of 100%. Any value lower than 100% means that the content is displayed smaller, any value larger than 100% that it is displayed bigger.
Firefox is not the first browser to display custom zoom indicators. Google Chrome displays a zoom icon (but not the zoom level after displaying it initially) in the address bar as well.
Vivaldi displays the zoom level in the status bar instead, and there all the time even if set to 100%. Microsoft’s Internet Explorer and Edge, and Opera, don’t display custom zoom levels in the interface(Opera displays it under menu but not directly).
The display of the custom zoom level acts as an indicator, but also as a reset option. Simply click on the indicator in the address bar to reset the zoom level to 100%.
Funny side note: The bug report on Bugzilla dates back to 2010 and makes mention of Firefox 4 specifically.
Currently, we don’t have any UI in the main window to indicate or adjust the zoom level. I think going all the way (similar to IE and Opera) and showing the zoom control always is a bit unnecessary and causes clutter, but on the other hand we need to have a way for people to adjust this more easily — and more importantly: be able to restore the zoom level to the default when they accidentally changed it.
Visualizing the custom zoom level is a good thing in my opinion. I sometimes zoom accidentally without realizing it (the difference between 100% and 90% or 110% is sometimes barely visible), and the indicator would help me realize it earlier.
It is probably only a matter of time before add-ons or styles become available that hide the display. (via Sören)