I'm currently on Firefox 56 and have seen the warning that many add-ons are going to break in 57, which is coming soon. I'm using one of the deprecated add-ons to increase the text size in tooltips, and am looking for another way to solve that problem in the new version.

I currently use Stylish to do this. Stylish is being replaced by Stylus, but Stylus cannot modify internal browser elements like the tooltip the way Stylish can. I know that Greasemonkey (soon ViolentMonkey) scripts can also modify CSS, but I wasn't able to find one that does this and I don't know enough about userscripting to write it myself. In my searches I also came across some add-ons that modify browser fonts, but none that specifically customize the tooltip.

Is there a userscript or non-legacy add-on that I can use to change the font size of tooltips in the browser? I don't want something that will "make everything bigger"; I've already tuned everything else. I just need a way to control tooltips.

Here is the Stylish CSS I'm currently using. (I didn't write this; I found it in a collection of user styles.)

  font-size: 16px !important; 
  font-family: tahoma, verdana !important;
  background-color: #FFFFE0 !important;
  color: #000000 !important;
  -moz-appearance: none !important;
  border-color: #000000 !important ;
  background-position: center center !important;
  background-repeat: no-repeat !important;
  background-attachment: scroll !important;

You've provided almost the complete answer with the code above: just add the script to userChrome.css. In Windows, that file resides in C:\Users\user name\AppData\Roaming\Mozilla\Firefox\Profiles\profile id.default\chrome, and if it doesn't exist, can be created there. On any OS, just enter the URL about:support to find the profile folder, and look for the folder chrome.

Profile folder

Mozilla has documentation for userChrome.css. Some of the uses I've found for this style-sheet is to make the selected tab more obvious, eliminate the tab-close button, change tab width and allow the sidebar to be shrunk below its preset limit. AFAIK, this CSS will still be functional in Firefox 57.

BTW, to search for Firefox extensions compatible with the Web Extension API, just search for the tag Firefox57.

  • Thank you! I did not know about userChrome. – Monica Cellio Nov 9 '17 at 16:55

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