Does not work with the current versions of Firefox, a fact not mentioned in the writeup.

It still doesn't work. Not on TB, or FF.

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Not working on Linux since FF moved to Quantum ((FF57?)

Periodically stops working. Now, April 2018 it is not fixed for weeks ...
The wanhunglo fix mentioned below works!

The thunderbird version of this addon breaks regularly rendering TB unusable because of the tiny fonts. I URGE ANYONE TO GO https://bugzilla.mozilla.org/show_bug.cgi?id=1453928 REGISTER AND UPVOTE THE BUG/COMMENT SO THAT THUNDERBIRD ADDS A FONT INCREASE OPTION BY DEFAULT

Once again not working anymore, because the id!ot author has built in a 90 day time limit after which the addon silently fails. Change build date (unix timestamp) or remove the check function in line 1382 of bootstrap.js to make it work again. Or visit wanhunglo (dot) com to download a fixed version.

Why is this addon still listed? Reported several times, this sh!t has been happening for the past three "updates" every single time!

absolutely not working extension

No funciona desde la última gran actualización

doesn't work with quantum.

Version 56, in Thunderbird 52.6.0 (64 bits) on MacOS shows no entry in tool menu neither it shows the button in the status bar. Thus, it cannot be opened !! Unusable :(

I'm using FF 52 and went as far back to v51 of this addon trying to find one that works. None did. Apart from the entry in the addon manager, there was no sign that it had installed - no toolbar option, no status bar icon. Nothing.

On Linux I can't change the font family.

Add on does not work with FF Quantum. All the advice I find on any of these pages involves files, extensions, changing this and that in your computer. You need to be a damn programmer to figure it out! Mozilla just create a simple easy to use and understand way for us to increase the size of the text in the Firefox menus. It was there before you can do it again. I have computer glasses and this is causing eye strain!!

I am so glad this was updated for Thunderbird, now if we could only get a version that works with the Waterfox browser which I just switched to today from Firefox 56 since I don't like Quantum and all my addons seem to work so far except for this one. I can't get any of the suggested fixes to work, even deleting the expiration date in the Theme Font Changer xpi file. Waterfox is suppose to open an independent browser add-on store so maybe that will help the issue.

Thanks for the hard work that goes into these addons, they make life noticeably less annoying.

It isn't working in the latest update of Firefox. FIX It already, millions of individuals with low vision depend on you

it doesn't work at all wih the latest t-bird. shame on Mozilla.

This addon is dead. I found a replacement for me - Zoom Page WE. If you just looking for scaling or zooming features, you should try this one.

No longer works on current versions of Firefox.

A Call For Help ~ TFSC Needs to be Fixed or Remade - Don't give up on this Add-On

This is a sorely needed add-on that many many people have came to rely on. I'm not here to blame Baris for an add-on that doesn't work but to mention how by this time Mozilla should have come with an 'In Built' version of this TFSC function as PART of Firefox itself. It's hard to believe that after all of this time, and all the DREADED news of FF57 Quantum coming that Mozilla could have helped the plethora of users relying on this add-on as a FUNCTION of Firefox. In a way, Baris is getting thumped for an add-on function that so many ppl believe should be part of the Firefox 'Preferences' BY NOW being that so many relied on it to even see what they were doing here while using THIS browser. Shame on YOU Mozilla for not filling in to help this roll-out of FF57. Many of us are still hoping with all our might that Baris can restore this OR some other developer can aid by filling in where Baris left off. What the Hell happened here??? This is really such a sad situation for the 'Visually impaired' users & the folks who view their net viewing several feet back from their TV-Monitor to enjoy the internet.

All of the browser Text on tabs and ALL of the Menu text on drop downs were afftected making it one heck of s strain to use Firefox. So OUR hope is that someone HEARING our PLEA shines a light on this situation and either puts TFSC back to it's optimum function OR can get a fire built under Mozilla's butt to build this Function into Firefox itself. Please______

03-18-19 I still come in here 'hoping' that someone will pick up the ball & run with it in getting this add-on back into usefullness. FF57 was a long time ago.