20 years with Yahoo - no problems. Install Font Size Changer - No iconsā¦ Draw your own conclusion.
I donāt have a clue where I installed it from. It came up, I thought it looked good, I installed it and have regretted it ever since 
Sorry, I didnāt attach the example from your siteā¦
There are 10 kinds of people in the world:- People who know binary and people who donāt.
What is the exact name of the add-on? Is it https://addons.mozilla.org/en-US/firefox/addon/theme-font-size-changer/?
Have you tried https://support.mozilla.org/en-US/kb/add-ons-and-extensions-faq#w_how-do-i-disable-or-uninstall-an-add-on ?
This is the requester that comes up when I click on itsā iconā¦
If this is a different one then I apologiseā¦ There are 10 kinds of people in the world:- People who know binary and people who donāt.
Hi, No further comment? Are you even going to look into the matter? So the same as before? A couple of responses then forget it? 
Most probably because you didnāt answer all of the questions you have been asked.
Any further comment or is that it?
Aside: TheOne you got a stressful job man 
I have diligently answered everything I have been asked. Any omission is unintended. The last question was answered with a snapshot (2 actually accidentally) 
of the App requester?
Regards,
Louwin
Can you post a screenshot of your add-on manager?
Is this what you want?
Not sure, is there also one listed in āExtensionsā?
Either way you should disable everything with that same and see if that resolves your issue.
Iāve attached snapshots of Extensions and Plugins. I donāt use any services.
I will try to disable everything on Friday (my day off). I WILL try this but donāt expect it to make a difference as it WAS working perfectly with whatever other plugins/extensions/appearance addons I HAD till I added āTheme Font & Size Changerā.
I hadnāt added ANY addons for months(if not years) till I added TF&SC. I immediately noticed the problem with Yahoo then other web pages. Even YOUR page(forum?) has the problem.
Yahoo seems the most affected, about 26 icons have gone missing on my Yahoo Mail page. I could live with the missing icons but the loss functioning of the icons is a different matter. Some icons work but VERY restrictedly. For instance, the āDeleteā mail icon works if I click the bottom line of the box.
Also strange is I have updated to Windows 10 from 8.1 and the problem persisted from 8.1 to 10.
Thanks for your response,
louwin
There are 10 kinds of people in the world:- People who know binary and people who donāt.
Why donāt you just disable āTheme Font & Size Changerā and be done with it, then?
Okay. I have disabled everything, everywhere (extensions, Appearance and Plugins). Closed Firefox. Restarted Firefox and the problem persists.
The attachment if the bottom of my current reply (this one!) showing the missing icons.
Sorry, what now!?
Regards,
Louis
There are 10 kinds of people in the world:- People who know binary and people who donāt.
If you want to avoid resetting your whole main profile, then you can try creating a new profile and see if it works there.
If it works there, then we can either carefully sync to that one by one to see what breaks it.
If it doesnāt work there, then you have like an anti-virus or something messing.
To create a new profile: https://addons.mozilla.org/en-US/firefox/addon/profilist/
I havenāt done ANYTHING else in the last week but my icons in Yahoo are back!!!
The last thing I did was to disable everything. Have to enable things and see if the problem comes back???
There are 10 kinds of people in the world:- People who know binary and people who donāt.
Very interesting thanks for sharing man, let us know what it was, so other people that run into the same problem can get the help. Ideally you can report what broke it to the author and he can fix for compatibility.
The only thing that comes to mind is Firefox got updated?
