Twitter
Twitter
[Cueball with a handheld device sits on an office chair.] Device: Beep beep
Device: On Twitter feeds
Device: Beep beep
Device: An odd regression:
Device: Beep beep
Device: Ancient memes
Device: Beep beep
Device: Find new expression
Device: Beep beep
Device: Burma-shave

This comic plays off of an old shaving cream product's Burma-Shave advertising campaign employed on American highways from 1925 to 1963 . These ads used short poems, each line arranged sequentially on a sign along a highway, the last line always being "Burma Shave," the name of the shaving cream. Originally, these ads only described the product, but others included driving safety messages.
Twitter is a messaging service where your messages are restricted in length, so to get a longer essay sent, you will need to break it up in smaller fragments — like the Burma-Shave messages, although the whole of the text of this comic is considerably less than 140 characters and would not need to be broken up on Twitter.
Cueball gets five messages from Twitter on his device that give the following message: On Twitter feeds - An odd regression: - Ancient memes - Find new expression - Burma-shave.
This relates that this old way (ancient-memes) of getting a message through when only having a limited space now again (an odd regression) flourishes on Twitter feeds - Burma-shave...
Firefox 2 had a long standing annoying bug where only the initial part of the title text were shown as a tool-tip, creating a "Burma-Shave" effect of only being able to see some of the text. Unlike Burma-Shave, where you would see the rest of the text as you were driving down the highway, Firefox didn't actually show you the rest of the text unless you right-clicked show-property, and you would be able to see a sideways scrollable field of the title-text in the properties for the image.
The joke in this title text is composed of five broken tool-tips from Firefox, and the message is that you should upgrade your browser from Firefox 2. Any other browser would do in order to improve your reading experience when browsing through xkcd!
[Cueball with a handheld device sits on an office chair.] Device: Beep beep
Device: On Twitter feeds
Device: Beep beep
Device: An odd regression:
Device: Beep beep
Device: Ancient memes
Device: Beep beep
Device: Find new expression
Device: Beep beep
Device: Burma-shave
